How can I apply styles to a label whose checkbox is checked using only CSS?

Question

Let's say I have a basic webpage:

<LABEL ID="THE_LABEL" FOR="THE_CHECKBOX"><INPUT TYPE=checkbox ID="THE_CHECKBOX"/> Blue when checked!</LABEL>

Now let's say that I want the label text to be red when it's unchecked and blue when it's checked. How would I do this? I want something as basic as the following. Here, I use a hypothetical operator "<", which would mean "has the child", but of course it won't work, as there's no such operator:

#THE_LABEL{
  color:red;
}
#THE_LABEL < #THE_CHECKBOX[checked]{
  color:blue;
}

Everything but the theoretical "<" is valid CSS, which makes me wonder if there's a real way to achieve this behavior. Does anyone know of a valid CSS 3 (or lower version) way to style a label based on the state of its checkbox, without using JavaScript?

Answer 1

You shouldn't be putting the input field within the label.

Since the contents of the label appear after the checkbox, just make your HTML this way:

    <INPUT TYPE=checkbox ID="THE_CHECKBOX"/> 
    <LABEL ID="THE_LABEL" FOR="THE_CHECKBOX">Blue when checked!</LABEL>

​

And then use this CSS:

#THE_LABEL {
    color: red;
}

#THE_CHECKBOX:checked + #THE_LABEL {
    color: blue;
}​

Live demo

The + is a sibling selector. It is not supported by IE8 and below.