JSFiddle - React, Tailwind, and code Playground

HTML

<select id="sites">
    <option value="http://www.mycity.rs">www.mycity.rs</option>
    <option value="http://www.blic.rs">www.blic.rs</option>
    <option value="http://www.b92.nedst">www.b92.net</option>
    <option value="http://www.google.rs">www.google.rs</option>
</select>
    
<iframe src="" id="load_site" style="display: none;"></iframe>

CSS

iframe { border: 0px; }

JavaScript

$("#sites").change(function(){
    $("#load_site").attr("src",$("#sites").val()).css("display","block");
});