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CSS3 selector priority rules

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Release： 2024-02-19 14:51:06

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CSS3 selector priority rules

CSS3 Selector Priority Order

In CSS, the priority of a selector determines which rule will be applied to an element. When multiple rules have the same priority, they are applied in the order in which they appear. For rules with different priorities, CSS uses a specific algorithm to determine which rule is ultimately applied. Below we will introduce the order of selector priorities in CSS3 and provide specific code examples.

In CSS, the priority of a selector is determined by the following factors:

Inline styles: Inline styles are styles that are applied directly to HTML elements. This is achieved by adding the style attribute. It has the highest priority.

For example:

<div style="color: red;">This is a red text.</div>

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ID selectors (ID selectors): ID selectors are matched by the id attribute of the element and start with the # symbol.

For example:

<div id="myDiv">This is my div.</div>

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#myDiv {
  color: blue;
}

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Class selectors, Attribute selectors and Pseudo-class selectors (Class selectors, Attribute selectors and Pseudo-class selectors): These selectors pass Class name, attribute or pseudo-class to match elements. Class selectors start with the . symbol, attribute selectors are wrapped in square brackets [], and pseudo-class selectors start with a colon:.

For example:

<div class="myClass">This is my class.</div>

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.myClass {
  color: green;
}

[priority="high"] {
  font-weight: bold;
}

a:hover {
  text-decoration: underline;
}

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Element selectors and Pseudo-element selectors: These selectors match by element name or pseudo-element element. Element selectors use the element name directly, and pseudo-element selectors start with the :: symbol.

For example:

<p>This is a paragraph.</p>

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p {
  font-family: Arial;
}

p::first-letter {
  font-size: 24px;
}

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If multiple selectors with the same priority appear, CSS3 specifies the order: inline style sheet> ID selector> class selector, Attribute selectors and pseudo-class selectors> Element selectors and pseudo-element selectors.

In actual use, we often encounter selector conflicts. At this time, we need to resolve the conflict according to the priority of the selector. Here is an example:

<!DOCTYPE html>
<html>
<head>
  <title>CSS3 Selector Priority Example</title>
  <style>
    .myClass {
      color: blue;
    }

    #myDiv {
      color: red;
    }

    p {
      color: green;
    }
  </style>
</head>
<body>
  <div id="myDiv">
    <p class="myClass">This is a paragraph inside a div.</p>
  </div>
</body>
</html>

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In the above example, the div element's id is "myDiv", the paragraph element p has the class name "myClass", and the p element is nested within the div element. Because the inline style sheet has the highest priority, the color of the paragraph element is red.

Summary: The priority order of selectors in CSS3 is inline style sheet> ID selector> class selector, attribute selector and pseudo-class selector> element selector and pseudo-element selector . When writing CSS styles, we need to pay attention to the priority of the selector to ensure that the style is applied to the element in the way we expect.

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