JSFiddle - React, Tailwind, and code Playground

HTML

<div id="dropdowns">
    <select multiple>
        <option>Option A</option>
        <option>Option B</option>
        <option>Option C</option>
        <option selected>Option D</option>
    </select>
</div>

CSS

/*#dropdowns option:checked {
    background: red;
}*/

#dropdowns option[selected] {
    background: red;
}