JSFiddle - React, Tailwind, and code Playground

HTML

<select>
    <option>one</option>
    <option>two</option>    
</select>

<input type="button" onclick="showPopup()" value="show"/>

<div id="popup">
    This is my popup
    <input  type="button" onclick="hidePopup()" value="hide"/>
</div>

<script>
var d = document;
function showPopup(){
    d.getElementById("popup").style.display = "block";
    updateSelects(d.getElementsByTagName("select"), "none");
}
function hidePopup(){
    d.getElementById("popup").style.display  = "none";
    updateSelects(d.getElementsByTagName("select"),  "inline");
}
    
function updateSelects(itens, value){
    for (i=0; i < itens.length;  i++) {
        itens[i].style.display = value;    
    }    
}
</script>

CSS

#popup {
    left: 0px;
    top: 15px;
    position: absolute;
    background: #ccc;
    width: 100%;
    height: 100%;
    display: none;
}