是否可以在 CSS3 选择器中使用 CSS 变量？

Question

I'm trying some experiments with CSS vars, and I couldn't get this to work or find any documentation about it. Does anyone know if it's possible to use a CSS var in a CSS3 selector?

I made the following example to explain what I'm trying to do. This example is Chrome only.

JSFIDDLE

http://jsfiddle.net/68Rrn/

CSS

:root {
    -webkit-var-count: 5; /* define my var! */
}

li {
    width:100px;
    height:100px;
    background-color:blue;
    display:inline-block;
    list-style:none;
}


ul li:nth-child(4) {
    background-color:red;
}

ul li:nth-child(-webkit-var(count)) { /* I can't get this working, is it even supported? I'm trying to target the 5th element with my var. */
    background-color:black;
}

HTML

<ul>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
    <li></li>
</ul>

Answer 1

Cascading variables (ie the var() notation) aren't defined for use with anything but property declarations, so no, they cannot be used in selectors. Judging by their name, this makes sense, since only property declarations can cascade, not selectors. From the spec :

A variable can be used in place of any part of a value in any property on an element. Variables can not be used as property names, selectors, or anything else besides property values. (Doing so usually produces invalid syntax, or else a value whose meaning has no connection to the variable.)