Style <select> element based on selected <option>

问题

Is it possible to style a select element based on what option is selected with CSS only? I am aware of existing JavaScript solutions.

I tried to style the option element itself, but this will give style only to the option element in the list of options, not to the selected element.

select[name=\"qa_contact\"] option[value=\"3\"] {
    background: orange;
}

http://jsfiddle.net/Aprillion/xSbhQ/

If not possible with CSS 3, will CSS 4 subject selector help in the future - or will this stay a forbidden fruit to CSS?

回答1:

Unfortunately, yes - this is something not currently possible with only CSS. As mentioned in the answers and comments to this question, there is currently no way to make the parent element receive styling based on its children.

In order to do what you're wanting, you would essentially have to detect which of the children (<option>) is selected, and then style the parent accordingly.

You could, however, accomplish this with a very simple jQuery call, as follows:

HTML

<select>
  <option value="foo">Foo!</option>
  <option value="bar">Bar!</option>
</select>

jQuery

var $select = $('select');
$select.each(function() {
    $(this).addClass($(this).children(':selected').val());
}).on('change', function(ev) {
    $(this).attr('class', '').addClass($(this).children(':selected').val());
});

CSS

select, option { background: #fff; }
select.foo, option[value="foo"] { background: red; }
select.bar, option[value="bar"] { background: green; }

Here is a working jsFiddle.

Back to the question about the future of selectors. Yes - the "Subject" selectors are intended to do exactly what you mention. If/when they ever actually go live in modern browsers, you could adapt the above code to:

select { background: #fff; }
!select > option[value="foo"]:checked { background: red; }
!select > option[value="bar"]:checked { background: green; }

As a side-note, there is still debate about whether the ! should go before or after the subject. This is based on the programming standard of !something meaning "not something". As a result, the subject-based CSS might actually wind up looking like this instead:

select { background: #fff; }
select! > option[value="foo"]:checked { background: red; }
select! > option[value="bar"]:checked { background: green; }

回答2:

A minimalist solution

This one has no JS dependency (you don't need jQuery or anything), it's a single line of code for a change event, merely an assignment that fetches a value into the DOM dataset. Also, in a production version you might want to add a data-chosen="something" to your select, in order to set the default option. But there are cases where it's not even necessary.

All we do here is make the select element aware of the current option. CSS can handle the rest.

    <select onchange=" this.dataset.chosen = this.value; ">
        ...
        ...
    </select>

This way, you can already attach CSS styling for your values, like this:

select[data-chosen='opt3'] { 
    border: 2px solid red;
}

See on CodePen.

Side note: it doesn't have to be the word "chosen", use any other if data-chosen is already allocated for some other purpose. The point is to get the value.

回答3:

So here is what I found on it being possible. The biggest issue is that after you have selected an element, the background color doesn't change because the select element isn't actually redrawn (seems more prevailant in IE - go figure). So even though you select a different option, that option isn't hightlighted in the list when you click the select element again.

To fix the redrawing issues in IE, it required changing the font-size by a minimal amount, +-.1. The other thing, which doesn't seem to be documented well, is that the pseudo class :checked does also work on select controls.

The fiddler to show the added css that makes it possible.

I only briefly played with it on Chrome and IE9, fyi.

EDIT: Obviously, you will need to set the [value="x"] to your desired value for specific option highlighting.

来源：https://stackoverflow.com/questions/16344583/style-select-element-based-on-selected-option