Are css attributes case sensitive?

CSS properties are not case-sensitive; because in CSS tag selectors and attribute selectors are case-insensitive, but class selectors and ID selectors may be case-sensitive, depending on the document language.

The operating environment of this article: windows7 system, HTML5&&CSS3 version, Dell G3 computer.

Q: Is CSS case-sensitive? (Is CSS case sensitive?)

This question is not that easy to answer.

Some books say that CSS is not case-sensitive, but this statement is actually not that strict. Because ID selectors and class selectors are case-sensitive, and selectors are the backbone of CSS.

For example, the following code

<p class="box"></p>
<p id="case"></p>

<style>
  /*有效*/
  p {
    width: 100px;
    height: 100px;
    border: 1px solid;
  }

  /*无效*/
  .Box {
    background: red;
  }
  
  /*无效*/
  #Case {
    background: blue;
  }
</style>

Recommended: "css video tutorial"

This is the code above Effect.

In the selector:

• ID and class selectors are case-sensitive
• Tag selectors and attribute selectors are not case-sensitive

Class selectors and ID selectors may be case-sensitive. This depends on the language of the document. HTML and XHTML define class and ID values ​​as case-sensitive, so the case of class and ID values ​​must match the corresponding values ​​in the document.

—— W3C

recommends using lowercase letters.

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