Why is there a backslash before \"31\" in the CSS code `.container.\\31 25\\25`?

What is the Meaning of .container.31 2525 in CSS?

In CSS, the backslash character () serves multiple purposes:

• Character Escape: It cancels the special meaning of certain characters, such as the percentage sign (%).
• Unicode Codepoint Reference: When followed by six hexadecimal digits, it represents a specific Unicode character.

In the given code:

<code class="css">.container. 25 {
  /* ... */
}</code>

• The backslash () before "31" cancels the special meaning of the number, allowing the class name to start with a numerical digit.
• The "31 2525" sequence represents three Unicode characters: "1" (U 0031), "%" (U 0025), and again "%" (U 0025).

Unicode Meaning:

Combining the Unicode characters yields "125%". This suggests that the class name is used to style elements with a width of 125% of the container.

Alternative Notation:

The same result can be achieved using the following alternative notation without using backslashes:

<code class="css">.container[class ~= "125%"] {
  /* ... */
}</code>

In CSS, identifiers (class names, element names, etc.) must not start with a digit, two hyphens, or a hyphen followed by a digit. However, using the backslash escape allows you to override this restriction.

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