CSS

CSS stands for Cascading Style Sheets, which is a style sheet language used for describing the presentation of a document written in HTML or XML. It is used to add style and layout to web pages, including fonts, colors, spacing, and other visual effects.

Here's an example of CSS code:

In this example, the CSS code sets the background color of the body element to light gray (#f2f2f2), the font family to Arial or sans-serif, the color and font size of the h1 element, and the color and line height of the p element.

CSS stands for Cascading Style Sheets. It is a language used for describing the presentation or style of a document written in HTML or XML. CSS is used to control the layout, typography, color, and other visual aspects of web pages. For example, the following CSS code changes the color of all paragraphs in an HTML document to red:

p { color: red; }

CSS (Cascading Style Sheets) is a styling language used for describing the presentation of a document written in HTML or XML. The main purpose of CSS is to separate the document's content from its presentation, making it easier to maintain and update the layout and style of multiple web pages simultaneously. By using CSS, web developers can apply consistent styles to all pages of a website, control the layout of web pages, adjust the font size and color, add animations and effects, and more.

For example, the following CSS code can be used to set the font size and color of the text in a paragraph element:

p { font-size: 18px; color: #333; }

This code selects all p elements and applies a font size of 18 pixels and a color of dark gray (#333) to the text inside the element.

There are several benefits of using CSS in web development:

1. Separation of Concerns: CSS allows separation of visual presentation from HTML markup and JavaScript behavior, making it easier to manage and maintain code.
2. Consistency: CSS allows for consistent styling across an entire website, making it easier to maintain a unified visual identity.
3. Faster Page Load Times: By separating style information into external style sheets, CSS allows for faster page load times because the browser can cache the style information.
4. Flexibility: CSS allows for greater flexibility and control in styling web pages. Developers can use CSS to create layouts, style text, add animations, and much more.
5. Accessibility: CSS allows for better accessibility for users with disabilities by providing greater control over font size, color contrast, and other visual elements.

There are three versions of CSS, which are:

1. CSS1: It was the first version of CSS that was introduced in 1996. It was limited in functionality and only supported a few basic styles and selectors.
2. CSS2: It was introduced in 1998 and added more advanced features like media queries, support for absolute and relative positioning, and the ability to use external style sheets.
3. CSS3: It was introduced in 1999 and is the most current version of CSS. It added even more advanced features like transitions, animations, and 3D transformations, as well as new selectors and properties.

Example:

In CSS, selectors are patterns used to select the HTML elements to apply styles. There are different types of selectors:

1. Element selectors: Select elements based on their tag name. For example, p selector selects all the <p> elements on the page.
2. Class selectors: Select elements based on their class attribute. For example, .example selector selects all the elements with class="example".
3. ID selectors: Select elements based on their id attribute. For example, #example selector selects the element with id="example".
4. Attribute selectors: Select elements based on their attributes. For example, [type="text"] selector selects all the elements with type="text" attribute.
5. Pseudo-class selectors: Select elements based on their state or position in the document. For example, :hover selector selects an element when the mouse hovers over it.
6. Pseudo-element selectors: Select parts of an element or insert content before or after an element. For example, ::after selector inserts content after the selected element.

Example:

You can apply CSS to an HTML document by either including the CSS code in a <style> element in the head section of the HTML document or by linking an external CSS file using the <link> element.

Here is an example of including CSS code in a <style> element in the head section of an HTML document:

And here is an example of linking an external CSS file using the <link> element:

In this example, the CSS code is contained in a separate file called "style.css", which is linked to the HTML document using the <link> element.

The syntax for adding CSS to an HTML document involves using the <style> element in the document head to define the CSS rules and properties, and then using CSS selectors to target specific HTML elements in the body of the document.

Here's an example of the syntax for adding CSS to an HTML document:

In this example, the CSS rules for the h1 and p elements are defined inside the <style> element in the document head. The color and font-size properties are used to style the text in the h1 and p elements. The CSS selectors h1 and p target the h1 and p elements respectively in the body of the document.

To create a CSS rule, you need to define a selector and then apply one or more style declarations within curly braces. The basic syntax of a CSS rule is as follows:

selector {
 	property1: value1;
  	property2: value2;
  	/* more properties and values */
}

Here, the selector is used to target one or more HTML elements, and the style declarations inside the curly braces define how those elements should be styled. For example, to change the font color of all paragraphs in an HTML document to blue, you can use the following CSS rule:

p { color: blue; }

This targets all <p> elements and sets their text color to blue.

Inline, internal, and external CSS are different ways of applying styles to HTML elements.

• Inline CSS: Inline CSS is applied directly to an individual HTML element using the style attribute. Inline styles have the highest specificity and will override external and internal styles.
  Example:


• Internal CSS: Internal CSS is defined within the <style> element in the head section of an HTML document. The styles defined in internal CSS will apply to all elements on the page unless overridden by an inline or external style.
  Example:
• External CSS: External CSS is defined in a separate .css file and linked to the HTML document using the <link> element. External styles can be applied to multiple HTML documents, and the styles will only apply to the elements specified in the CSS file.
  Example:

In general, external CSS is the preferred way to apply styles to an HTML document as it allows for separation of concerns and reusability of styles across multiple pages.

To override CSS styles, you can use specificity, inheritance, or the !important rule.

• Specificity: This refers to the weight of the selector used to apply a style. A more specific selector will override a less specific one. For example, a selector with an ID has a higher specificity than a selector with a class.
• Inheritance: Some properties are inherited from parent elements. If a child element has the same property set as its parent, it will inherit that value unless you override it with a more specific selector.
• !important: Adding !important after a style rule will give it the highest priority, overriding any other styles.

Here's an example of how to override a CSS style using specificity:

In this example, the original style sets the color of all p elements to blue. To override this, we use a more specific selector that targets only p elements inside an element with the ID my-text. The color property is set to red, and because this selector is more specific than the original one, it will be applied instead.

In CSS, specificity is a mechanism that determines which style rule applies to an element. It refers to the weight or importance of a selector in relation to other selectors targeting the same element.

Specificity is calculated based on the combination of selectors used to target an element. Selectors with a higher specificity value will override those with a lower value. The specificity of a selector is determined by four factors:

1. Type selectors have a specificity of 1
2. Class selectors have a specificity of 10
3. ID selectors have a specificity of 100
4. Inline styles have a specificity of 1000

Here's an example to illustrate specificity:

In ths example, the p element has a class of my-class and an ID of my-id. The color of the text in the p element will be green because the selector with an ID has the highest specificity. If we removed the #my-id selector from the CSS, the text color would be blue because the .my-class selector has a higher specificity than the p selector.

In CSS, pseudo-classes are keywords used to define a special state of a HTML element. These states may not be represented by the document's structure, but are rather based on user interaction, history, or the element's position in the document. Some common examples of pseudo-classes include :hover, :active, and :focus.

For example, the :hover pseudo-class is used to apply styles to an element when the user hovers their mouse over it. Here's an example:

Pseudo-elements in CSS are keywords that represent virtual elements that don't exist in the HTML markup. They allow you to style a specific part of an element's content, such as the first letter or first line, without adding extra HTML markup. Pseudo-elements are represented by a double colon (::) notation in CSS.

For example, to apply a different style to the first letter of a paragraph, you can use the ::first-letter pseudo-element selector like this:

This would make the first letter of every paragraph on the page have a font size of 200% and be bold.

The box model in CSS is a design concept that treats each HTML element as a rectangular box, comprising of four areas - content, padding, border, and margin. The content area is the actual content or text of the element, while the padding area surrounds the content and provides space between the content and the border. The border area is a line that goes around the padding and content, while the margin area is a transparent area that surrounds the border, providing space between the element and other elements on the page. The box model is important for understanding layout and spacing in CSS.

For example, consider the following CSS code for a div element:

In this code, the div element has a width of 200 pixels, height of 100 pixels, 10 pixels of padding, a 2-pixel solid black border, and a margin of 20 pixels. This means that the actual size of the box will be 244 pixels wide (200px content width + 2px left border + 2px right border + 10px left padding + 10px right padding), and 152 pixels high (100px content height + 2px top border + 2px bottom border + 10px top padding + 10px bottom padding), with 20 pixels of space around the outside of the box due to the margin.

To adjust the box model in CSS, you can use the following properties:

1. padding: adds space inside the border of an element
2. border: sets the border around an element
3. margin: adds space outside the border of an element

For example, if you want to add 10 pixels of padding and 5 pixels of margin to a div element, you can use the following CSS code:

This will add a 10 pixel padding inside the div element, a 1 pixel solid black border around the div, and a 5 pixel margin outside the div element.

There are several display properties in CSS that allow you to control the layout and behavior of HTML elements:

1. block: This property creates a block-level element that takes up the full width of its parent container. It starts on a new line and can have height, width, padding, margin, and border.
   
   Example:

   div { display: block; }

2. inline: This property creates an inline-level element that only takes up as much width as necessary. It cannot have width, height, margin-top, or margin-bottom.
   
   Example:

   span { display: inline; }

3. inline-block: This property creates an inline-level element that can have width, height, padding, margin, and border.
   
   Example:

   button { display: inline-block; }

4. flex: This property creates a flexible container that allows you to control the alignment, direction, order, and size of its child elements.
   
   Example:

   .container { display: flex; flex-direction: row; }

5. grid: This property creates a grid container that allows you to control the placement and size of its child elements in a grid format.
   
   Example:

   .container { display: grid; grid-template-columns: 1fr 1fr 1fr; }

6. none: This property hides the element and its space in the layout.
   
   Example:

   .hidden { display: none; }

These are some of the most commonly used display properties in CSS, but there are several others as well.

In CSS, block, inline, and inline-block are display properties that define how elements should be displayed on a web page.

• Block elements take up the full width of their parent container and create a new line after themselves. They can have a height and width specified and can contain other elements. Examples of block elements include <div>, <h1>-<h6>, <p>, and <ul>.
• Inline elements, on the other hand, do not create a new line after themselves and only take up as much width as their content requires. They cannot have a height or width specified and cannot contain other block-level elements. Examples of inline elements include <a>, <span>, <img>, and <strong>.
• Inline-block elements are similar to inline elements, in that they do not create a new line after themselves, but they can have a height and width specified and can contain other elements. Examples of inline-block elements include <button> and <input>.

Here's an example of how the three display properties work:

In this example, the block element takes up the full width of its parent container and creates a new line after itself. The inline element only takes up as much width as its content requires and does not create a new line after itself. The inline-block element does not create a new line after itself, but takes up a specified width and height, and can contain other elements.

The position property in CSS specifies how an element should be positioned on a webpage. There are several position values:

1. static: This is the default value, where the element is positioned according to the normal flow of the webpage.
   
   

   div { position: static; }

2. relative: This positions the element relative to its normal position in the webpage.
   
   

   div {
     position: relative;
     top: 20px;
     left: 30px;
   }

3. absolute: This positions the element relative to its closest positioned ancestor, if any; otherwise, it is positioned relative to the initial containing block.
   
   

   div {
     position: absolute;
     top: 50px;
     left: 80px;
   }

4. fixed: This positions the element relative to the viewport. It stays in the same place even if the page is scrolled.
   
   

   div {
     position: fixed;
     top: 0;
     right: 0;
   }

5. sticky: This is a hybrid of relative and fixed positioning. The element is positioned relative to its normal position in the webpage, but will stick to the viewport when scrolled past.
   
   

   div {
     position: sticky;
     top: 0;
     padding: 10px;
     background-color: #fff;
   }

The position property in CSS is used to specify the type of positioning method to be used for an element. There are four values for the position property:

1. static: The default value. The element is positioned according to the normal flow of the document. This value cannot be used with the top, bottom, left, or right properties.
2. relative: The element is positioned relative to its normal position, so the top, bottom, left, or right properties can be used to specify how far to offset the element from its normal position.
3. absolute: The element is positioned relative to its nearest positioned ancestor (i.e., an ancestor with a position other than static). If no positioned ancestor is found, the element is positioned relative to the initial containing block. The top, bottom, left, or right properties can be used to specify the offset.
4. fixed: The element is positioned relative to the viewport (i.e., the browser window), so the top, bottom, left, or right properties can be used to specify the offset. The element remains in the same position even if the page is scrolled.

Example:

To center an element in CSS, you can use the text-align property or the margin property. Here are some examples:

1. Horizontally centering a block-level element:
   
   
2. Vertically centering a block-level element:
   
   
3. Centering a block-level element both horizontally and vertically:
   
   
4. Centering an inline element using the text-align property:
   
   

The float property in CSS allows you to move an element to the left or right of its container, allowing other elements to flow around it.Here's an example:

In this example, the div with class floated is floated to the left, which causes the div with class content to flow around it. The float property is set to left, and a width and height are specified to give the floated element some dimensions. The background colors are set for visibility.

The clear property in CSS specifies which sides of an element should not be adjacent to floating elements. This property is often used after the float property to ensure that the following elements are not positioned adjacent to the floated elements.

The clear property can have the following values:

• none (default): the element is allowed to be adjacent to both left and right floating elements.
• left: the element is not allowed to be adjacent to left floating elements.
• right: the element is not allowed to be adjacent to right floating elements.
• both: the element is not allowed to be adjacent to any floating elements.

Example:

In this example, the float-left class is used to float an element to the left. The clear class is then used on a following element to ensure that it is not positioned adjacent to the floated element, regardless of whether it is floated left or right.

To create a navigation menu in CSS, you can use the HTML list element <ul> and <li> to create a list of menu items. Then, you can use CSS to style the list items as inline-block elements to create a horizontal menu.

Here is an example:

In this example, the <nav> element is used to wrap the <ul> element to indicate that this is a navigation menu. The list-style, margin, and padding properties are used to remove the default bullet points, margins, and padding from the list. The text-align property is used to center the list items horizontally.

The display property with the value of inline-block is used to make the list items display horizontally. The margin property with the value of 0 10px is used to create some space between each menu item.

The <a> elements are styled as block-level elements and given some padding to make them clickable. The text-decoration property is used to remove the default underline from the links. Finally, the :hover pseudo-class is used to change the background color and text color of the links when they are hovered over.

The z-index property in CSS determines the stacking order of positioned elements that overlap each other. The higher the z-index value, the more it will be on top of other elements with a lower z-index value.

For example, suppose you have two overlapping elements, a div with a z-index of 1 and a p with a z-index of 2. The p element will be on top of the div element because its z-index value is higher.

The syntax for using the z-index property is as follows:

selector { z-index: value; }

Where selector is the element you want to apply the z-index property to, and value is the numeric value for the z-index.

Here's an example:

In this example, the p element will be on top of the div element because it has a higher z-index value.

To create a responsive design in CSS, you can use a combination of media queries and flexible units like percentages or viewport units.

Here's an example:

In this example, the base styles define a .box element with a width of 50%, a height of 200px, and a blue background color.

Then, using media queries, the styles are adjusted for different screen sizes. When the screen width is 768px or less, the .box element will have a width of 100%, a height of 150px, and a red background color. When the screen width is 480px or less, the .box element will have a width of 100%, a height of 100px, and a green background color.

By using media queries and flexible units, this design can adjust to different screen sizes and provide a better user experience on different devices.

Media queries in CSS allow you to apply different styles based on the characteristics of the device or screen that your web page is being viewed on. This is especially useful for creating responsive designs that adapt to different screen sizes and orientations.

Here's an example of a media query that applies a different background color to a page when viewed on a device with a maximum width of 600 pixels:

In this example, the @media rule specifies that the styles within the curly braces should only be applied if the screen width is 600 pixels or less. The body selector then applies the background-color property with the value lightblue. By using media queries, you can create styles that adjust to different devices and screen sizes, resulting in a better user experience.

The flexbox layout is a CSS layout mode that provides a flexible way to arrange elements within a container. It enables you to create complex layouts with ease and without relying on floats, position, or table display modes. With flexbox, you can align and distribute elements both vertically and horizontally.

Here is an example of how to use the flexbox layout in CSS:

In the above example, we have a container element with a display property set to flex, which enables the flexbox layout. The flex-direction property is set to row, which means that the child elements will be arranged in a row. The justify-content property is set to center, which centers the child elements horizontally within the container. The align-items property is set to center, which centers the child elements vertically within the container. Finally, we have an .item class with a flex property set to 1, which means that the item will grow or shrink to fill the available space.

CSS Grid Layout is a two-dimensional layout system that allows you to create complex, responsive layouts with rows and columns. It provides a way to arrange elements into a grid of rows and columns, allowing for easy alignment and positioning of content.

Here is an example of how to create a basic grid layout:

In this example, we create a container element with a class of "grid-container" that uses the display: grid property to enable grid layout. We define three columns with equal widths using the grid-template-columns: 1fr 1fr 1fr property, and we set the row height to "auto" using grid-template-rows: auto. We also add a 10px gap between the grid items using grid-gap: 10px.

Each child element of the container, with a class of "grid-item", is automatically placed into the grid. We can style the grid items as desired, such as by setting a background color and padding.

In CSS, padding and margin are two properties that affect the spacing around an element. The key difference between them is that padding is the space between the element's content and its border, while margin is the space between the element's border and the neighboring elements or the outer container.

For example, let's say we have an HTML element with a width of 200px and a height of 100px. If we apply a padding of 10px, the total size of the element will be 220px by 120px, with 10px of padding around the content. On the other hand, if we apply a margin of 10px, the element will still be 200px by 100px, but there will be 10px of space between the element's border and the neighboring elements or outer container.

Here's an example of the CSS code for applying padding and margin to an HTML element:

To add a background image in CSS, you can use the background-image property along with the URL of the image file.

Here is a simple example:

This will set the background image of the body element to the image located at "path/to/image.jpg". You can also specify other properties such as background-repeat, background-size, and background-position to control how the image is displayed.

To create a gradient background in CSS, you can use the background property with the linear-gradient() function. The linear-gradient() function creates a gradient that gradually transitions between two or more colors in a straight line.

Here's an example:

background: linear-gradient(to bottom, #ffffff, #000000);

This will create a gradient that starts at the top with white (#ffffff) and gradually transitions to black (#000000) at the bottom.

You can adjust the direction of the gradient by changing the to bottom value to another direction such as to right, to top, or to left.

You can also add more color stops to the gradient by specifying additional color values and percentage values. For example:

background: linear-gradient(to bottom, #ffffff, #ff0000, #000000);

This will create a gradient that starts at the top with white (#ffffff), transitions to red (#ff0000) in the middle, and then transitions to black (#000000) at the bottom.

You can add a border to an element in CSS using the border property. The border property allows you to set the width, style, and color of an element's border.

Here's an example:

div { border: 2px solid black; }

In this example, the div element will have a 2-pixel wide solid black border. The border property can also be used to set different values for each side of an element's border. For example, you can use the border-top, border-right, border-bottom, and border-left properties to set the top, right, bottom, and left borders of an element separately:

In this example, the div element will have a 2-pixel wide dashed red top border, a 1-pixel wide dotted blue right border, a 3-pixel wide solid green bottom border, and a 1-pixel wide double purple left border.

The border-box value in CSS is a box-sizing property that includes the content, padding, and border within the specified width and height of an element. This is in contrast to the default content-box value, which only includes the content within the specified width and height.

Using border-box can make it easier to size elements because you can specify their total size without having to calculate the extra space added by borders and padding.

Here's an example of using border-box in CSS:

In this example, the .box element has a width and height of 200px and 100px respectively. The padding adds 20px of space inside the box, and the border adds an additional 4px (2px on each side) around the outside of the box. With box-sizing: border-box, the total width and height of the box including the content, padding, and border is 200px by 100px, making it easier to calculate the size of the box.

You can create a drop shadow effect in CSS using the box-shadow property.

Here's an example:

The text-shadow property in CSS adds a shadow effect to text. It takes in four values: horizontal offset, vertical offset, blur radius, and shadow color.

Here's an example of using text-shadow:

In this example, the h1 element will have a text shadow with a horizontal offset of 2 pixels, a vertical offset of 2 pixels, a blur radius of 4 pixels, and a shadow color of black (#000000).

To change the font in CSS, you can use the font-family property. This property specifies the font family or font faces for text content.

Here's an example:

body { font-family: Arial, sans-serif; }

In this example, the font family is set to Arial, which is a sans-serif font. If Arial is not available, the browser will look for a sans-serif font installed on the user's computer.

You can also specify the font size, weight, and style using the font-size, font-weight, and font-style properties. Here's an example:

In this example, the h1 element is styled with a font family of Georgia, a font size of 2em, a font weight of bold, and a font style of italic.

The font-size property in CSS is used to set the size of the font in an element. It specifies the size of the font as a length value or a percentage of the parent element's font size.

Here's an example that sets the font size to 16 pixels:

In this example, all <p> elements will have a font size of 16 pixels. You can also use other length units, such as em or rem, or percentages, like 100% or 200%, to set the font size relative to other elements.

The font-weight property in CSS defines the weight or thickness of the font. The weight can range from 100 (thin) to 900 (bold) and can also be set to normal or bold for convenience.

Here is an example of setting the font-weight property in CSS:

In the example above, the h1 elements will have a bold font weight, while the p elements will have a thinner font weight of 300.

The line-height property in CSS is used to set the distance between lines of text within an element. It defines the amount of space between two consecutive lines of text and can be set in different ways, such as as a fixed value, a percentage, or a unitless value.

For example, to set a line-height of 1.5 for a paragraph element, you can use the following CSS rule:

This will increase the space between each line of text in the paragraph to 1.5 times the font size. Increasing the line-height can make text more readable and improve the overall design of a webpage.

You can align text horizontally and vertically using the text-align and vertical-align properties, respectively.

For example, to center align text within a div element, you can use the following CSS code:

To vertically align text within a div element, you can use the following CSS code:

This will display the text vertically aligned to the middle of the div element.

The text-decoration property in CSS is used to add or remove visual decoration to text. It can be used to add underlines, overlines, line-throughs, and even blinking effects to text. The common values for this property are none, underline, overline, line-through, and blink.

Here is an example:

This will add an underline to all the paragraphs in the HTML document.

The color property in CSS is used to set the color of the text content in an HTML element. The value of this property can be specified in various ways, including by color name, hexadecimal, RGB, or HSL values.

For example, to set the color of the text content of a paragraph element to red, you can use the following CSS code:

p { color: red; }

This will change the color of all paragraph elements to red. Alternatively, you can also use a hexadecimal value to specify the color, like this:

p { color: #FF0000; }

This will also set the color of all paragraph elements to red, using the hexadecimal representation of the color red.

To create an animation in CSS, you can use the @keyframes rule to define the animation and the animation property to apply it to an element.

Here's an example:

In this example, a red box with a size of 100 pixels is defined, and the animation property is used to apply the myanimation animation to it. The myanimation animation is defined using the @keyframes rule, which specifies the different stages of the animation.

The myanimation animation scales the box from its original size to 150% of its size, changes its background color to blue, and then scales it back to its original size. The animation takes 2 seconds to complete and repeats infinitely.

The transition property in CSS specifies how a CSS property should change over time during a transition. It is used to create smooth and gradual transitions between different styles.

The syntax for transition is as follows:

selector { transition: property duration timing-function delay; }

• property: specifies the CSS property that should be transitioned
• duration: specifies the duration of the transition in seconds or milliseconds
• timing-function: specifies the speed curve of the transition
• delay: specifies a delay before the transition will start

Here is an example that shows how to create a transition on the background-color property:

In this example, when the user hovers over the button, the background color changes from blue to red over a period of 0.5 seconds with an ease timing function.

To create a hover effect in CSS, you can use the :hover pseudo-class selector along with the CSS properties that you want to apply on hover.

Here's a simple example:

In this example, we have a button element styled with a green background color and white text. When the user hovers over the button, the background color transitions to a darker shade of green, creating a hover effect. The transition property is used to control the duration and easing of the transition between the two background colors.

To create a tooltip in CSS, you can use the ::before or ::after pseudo-elements along with the content property to add a tooltip text, and the position property to position it accordingly.

Here's an example:

In this example, we first give the container element a position value of relative, which allows us to position the tooltip text relative to the container. We then create the tooltip text using the ::before pseudo-element, and position it using the position, bottom, left, and transform properties. Finally, we use the opacity and transition properties to animate the tooltip text when the container is hovered over.

To create a dropdown menu in CSS, you can use a combination of HTML and CSS. The HTML would consist of a navigation menu and a nested list, while the CSS would control the positioning and visibility of the nested list.

Here's an example of how to create a basic dropdown menu in CSS:

This code will create a navigation menu with a dropdown list under the "Products" link. When you hover over the "Products" link, the nested list will become visible.

The box-shadow property in CSS allows you to add a shadow effect to an element. It takes a series of values that define the size, color, and type of the shadow.

Here's an example:

In this example, the .box element will have a shadow that is 2 pixels to the right and 2 pixels down from the element, with a blur radius of 4 pixels, and a color of black with an opacity of 0.5. The box-shadow property can also be used to create multiple shadows by adding additional values separated by commas.

The border-radius property in CSS is used to create rounded corners for an element. The value of border-radius determines the size of the rounded corners.

Here is an example:

.rounded { border-radius: 10px; }

In the above example, the .rounded class has a border-radius of 10px, which means that all four corners of the element will have a radius of 10px. You can also set different values for each corner individually, as follows:

In the above example, the .rounded class has different border-radius values for each corner of the element. The top-left corner has a radius of 5px, the top-right corner has a radius of 10px, the bottom-left corner has a radius of 15px, and the bottom-right corner has a radius of 20px.