JSFiddle - React, Tailwind, and code Playground

HTML

<select>
    <option value="mankind">Man kind</option>
    <option value="humankind">Human kind</option>
    <option selected value="animalkind">Animal kind</option>
</select>

CSS

select {
    padding: 5px;
    border: 1px solid blue;
    -webkit-transition: width 2s; /* Safari */
    -webkit-transition-timing-function: linear; /* Safari */
    transition: width 2s;
    transition-timing-function: linear;
}
select:hover {
    border: 1px solid red;
    width: 300px;
}