Can CSS Style a Select Element Based on its Chosen Option?

Style the Chosen: Can CSS Style a Select Based on the Selected Option?

Is it possible to customize the appearance of a select element based on the currently selected option? Despite the availability of JavaScript solutions, this question often arises.

Challenging the Impossible

Styling the element itself, as you attempted, modifies its appearance when it's present in the options list, but not when selected. CSS alone cannot target the selected element directly due to current technical limitations.

Subject Selector to the Rescue?

CSS 4's proposed subject selector may offer potential in the future. However, as of now, this feature remains unavailable.

The :has Pseudo-Class

While the :has pseudo-class can partially help, it's limited to styling the select based on HTML attributes and only when the option is explicitly selected initially. Its limitations become apparent when the user changes the selection, which modifies DOM properties without affecting the HTML attributes that CSS relies on.

A CSS-Only Solution

Despite the limitations of CSS, a clever solution exists. By introducing a data-chosen attribute with a value assignment in the onchange event, we can make the select element aware of the current option. This creates an opportunity for CSS to target and style based on the selected option.

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

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

This elegant solution empowers CSS to customize the select element's appearance based on the selected option without the need for JavaScript.

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