JSFiddle - React, Tailwind, and code Playground

HTML

<select name="mine" id="mine">
    <option value="#my1">Test1</option>
    <option value="#my2">Test2</option>
</select>

<div id="my1" class="my">
    <p>Some Text in 1</p>
</div>

<div id="my2" class="my">
    <p>Some Text in 2</p>
</div>

CSS

.my:not(.selected) {
    display: none;
}

JavaScript

document
    .querySelector('select')
    .addEventListener('change', function () {
        var elements = Array.prototype.slice.call(document.querySelectorAll('.my'), 0),
            target = document.querySelector(this.value);
        
        elements
            .forEach(function (elem) {
                if (elem === target) {
                    elem.classList.add('selected');
                } else {
                    elem.classList.remove('selected');
                }
            });
    });