JSFiddle - React, Tailwind, and code Playground

HTML

<div id="header">
    Better to stick 
</div>

<div id="content">
    content
</div>

CSS

*{
    margin: 0px;
    padding: 0px;
}
    #header{
        background-color: #1874CD;
        width: 100%;
        height: 70px;
        z-index: 2;
        position: relative;
    }

    

   #content{
       position: absolute;
       top: 0px;    
       left: 0px;
       background-color: #F5F5F5;
        width: 100%;
        height: 100%;  
        padding-top: 70px;        
    	-webkit-box-sizing: border-box; /* Safari/Chrome, other WebKit */
    	-moz-box-sizing: border-box;    /* Firefox, other Gecko */
      	box-sizing: border-box;     
    }