JSFiddle - React, Tailwind, and code Playground

CSS

#mainContainer{
    width: 400px;
    height: 200px;
    border: 2px solid green;
    margin-left: 20px;
}

.blocks{
    width: 100px;
    height: 100px;
    border: 1px solid black;
    float: left;
    margin-left: 20px;
    margin-top: 10px;
    
}

JavaScript

(function() {
    
    function create() {
       var mainContainer = document.createElement("div");
       mainContainer.id = "mainContainer";
       document.body.appendChild(mainContainer);
        
       for(var i = 0; i < 3; i++) {
           var divBlock = document.createElement("div");                
           divBlock.className = "blocks";
           mainContainer.appendChild(divBlock);       
       }
            
    }
    
    create();
    
}());