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What are CSS rulesets used for?

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Release： 2023-09-09 16:01:02

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What are CSS rulesets used for?

CSS stands for Cascading Style Sheets. It is used to style HTML elements. HTML is used to create or add content to web pages. After that, developers use CSS to render the HTML content in a specific style to make it look great.

The CSS rule set mainly contains two parts. One is a CSS selector and the other is a declaration block.

CSS selectors are used to select HTML elements, and the declaration block contains CSS properties in key-value format to be applied to HTML elements.

grammar

Users can use the CSS rule set to style HTML elements according to the following syntax.

selector {
   /* declaration block */
}

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In the above syntax, 'selector' can be the class name, id, etc. of the HTML element, which is used to select HTML elements. A declaration block contains multiple CSS properties and their values to apply to HTML elements.

Example 1 (CSS class name selector)

In the example below, we use the class name as the CSS selector when defining the CSS ruleset. The code below has three div elements with different class names. We selected each div element by its class name and applied a different CSS style, which the user can observe in the output.

<html>
<head>
   <style>
      .one {
         background-color: red;
         color: white;
         padding: 10px;
         margin: 10px;
         border: 1px solid green;
      }
      .two {
         background-color: green;
         color: white;
         padding: 10px;
         margin: 10px;
         border: 3px solid yellow;
      }
      .three {
         background-color: blue;
         color: white;
         padding: 10px;
         margin: 10px;
         border: 2px solid pink;
      }
   </style>
</head>
<body>
   <h2> Using the <i> class selector </i> in CSS ruleset </h2>
   <div class = "one"> One </div>
   <div class = "two"> Two </div>
   <div class = "three"> Three </div>
</body>
</html>

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Example 2 (CSS ID Selector)

In the example below, we use the id of the HTML element as the CSS selector when defining the CSS rule set. In HTML, two elements can never contain the same id.

Here, we have a div element with an id of "card", which contains two other div elements with an id equal to "content1" and "content2". We style all HTML elements by accessing them by their ID, which the user can observe in the output.

<html>
<head>
   <style>
      #card {
         width: 140px;
         height: 300px;
         background-color: grey;
         border-radius: 12px;
         border: 2px solid red;
         display: flex;
         justify-content: space-between;
         flex-direction: column;
      }
      #content1 {
         width: 100px;
         height: 100px;
         background-color: blue;
         border-radius: 12px;
         color: white;
         border: 2px solid red;
         margin: 20px;
      }
      #content2 {
         width: 100px;
         height: 100px;
         color: white;
         background-color: blue;
         border-radius: 12px;
         border: 2px solid red;
         margin: 20px;
      }
   </style>
</head>
<body>
   <h2> Using the <i> id selector </i> in CSS ruleset </h2>
   <div id = "card">
      <div id = "content1"> HTML </div>
      <div id = "content2"> CSS </div>
   </div>
</body>
</html>

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Example 3 (CSS Multiple Selector)

In the example below, we use multiple CSS selectors to apply the same CSS style to multiple HTML elements at once.

We have three

elements with different class names and IDs. In CSS, we use the “.text1, .text2, #para1” CSS selector to apply the same styles added in the declaration block to all HTML elements.

Additionally, we have selected all three HTML elements individually using class name and ID CSS selectors in order to apply different styles on different elements.

<html>
<head>
   <style>
      .text1,
      .text2,
      #para1 {
         margin: 10px;
         height: auto;
         padding: 10px;
         width: 200px;
      }
      .text1 {
         background-color: red;
         color: white;
         font-size: 2rem;
      }
      .text2 {
         background-color: green;
         color: red;
         font-size: 1.7rem;
      }
      #para1 {
         background-color: blue;
         color: white;
         font-size: 1rem;
      }
   </style>
</head>
<body>
   <h2> Using the <i> Multiple selector </i> in CSS ruleset </h2>
   <p class = "text1"> This is the first paragraph </p>
   <p class = "text2"> This is a second paragraph. </p>
   <p id = "para1"> This is the third paragraph. </p>
</body>
</html>

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Example 4 (CSS nested element selector)

In the following example, we introduce CSS’s nested selectors. In HTML, a div element contains multiple elements with the class name "link".

In CSS, we use the "div .link" CSS selector, which selects all HTML elements with the class name "link" and the descendants of the div element. If we use "div.link" as CSS selector, it will apply the style to all div elements with class name "link". Therefore, "div.link" and "div .link" are both different CSS selectors.

In the output, the user can observe that CSS styles are applied to all HTML elements that are descendants of the div element, but not to elements outside the div element.

<html>
<head>
   <style>
      div .link {
         color: red;
         text-decoration: none;
      }
   </style>
</head>
<body>
   <h2> Using the <i> nested selectors </i> in CSS ruleset </h2>
   <div>
      <a href = "#" class = "link"> Link1 </a>
      <a href = "#" class = "link"> Link2 </a>
      <a href = "#" class = "link"> Link3 </a>
   </div><br>
   <a href = "#" class = "link"> Link 5 </a>
</body>
</html>

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Example 5 (CSS pseudo-selector)

In this example, we demonstrate the use of CSS pseudo-selectors. There are many kinds of CSS pseudo-selectors, and we use some of them here.

Here, we have a "container" div element that contains 4 child elements with the "element" class name. We use the ":hover" pseudo-selector to change the background color of the "container" div element when the user hovers over the div element.

After that, we use the ':first-child', ':last-child' and ':nth-child()' CSS selectors and the '.element' selector to select the first child element, the last child element elements, and the nth child, respectively.

In the output, the user can observe that different CSS styles are applied to the first child, the last child, and the second child.

<html>
<head>
   <style>
      .container {
         height: 100px;
         width: 500px;
         background-color: blue;
         padding: 10px;
         display: flex;
         justify-content: space-around;
         border-radius: 12px;
         font-size: 1.2rem;
      }
      /* hover pseudo class */
      .container:hover {
         background-color: red;
      }
      /* first child pseudo class */
      .element:first-child {
         background-color: green;
         color: white;
      }
      /* last child pseudo class */
      .element:last-child {
         background-color: grey;
         color: black;
      }
      /* nth child pseudo class */
      .element:nth-child(2) {
         background-color: pink;
         color: green;
      }
   </style>
</head>
<body>
   <h2> Using the <i> pseudo selectors </i> in CSS ruleset </h2>
   <div class = "container">
      <div class = "element"> First Child </div>
      <div class = "element"> Second Child </div>
      <div class = "element"> Third Child </div>
      <div class = "element"> Fourth Child </div>
   </div>
</body>
</html>

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Users learned how to use different CSS rule sets in this tutorial. We use class name and id as selector. Additionally, we learned about using multiple CSS selectors and nested CSS selectors. In the previous example, we learned how to use pseudo-selectors from a CSS ruleset.

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