Style <select> element based on selected <option>

Pure CSS Method:-

You can style it if you want to apply style if empty value selected using :valid selector like the following code

Display in Red If Selected value is Empty

select > option {
  color: black;
  font-weight:initial;
}
select option[value=""] {
  color: red;
  font-weight:bold;
}
select[required]:invalid {
  color: red;
  font-weight:bold;
}
<select required name="fontSize">
<option value="">Please select</option>
<option value="9">9 px</option>
<option value="10">10 px</option>
<option value="11">11 px</option>
<option value="12">12 px</option>
<option value="13">13 px</option>
<option value="14">14 px</option>
<option value="15">15 px</option>
<option value="16">16 px</option>
</select>
<select required name="fontColor">
<option value="">Please select</option>
<option value="red" selected>Red</option>
<option value="green">Green</option>
<option value="blue">Blue</option>
</select>

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; }

Impossible? Hold my beer.

Make the select element aware of the current option. CSS can handle the rest. For this, all we need is a value assignment in the onchange event. With a little more effort you can also initialize the <select> tag by its original value; not included below but it's super easy, just give it a "data-chosen" property when composing the markup.

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

And now you can easily target & style it:

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

See on CodePen.

Side note: "chosen" is no magic word, just a descriptive name - it could be "SantaClaus". It would also look better that way.


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.

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