JSFiddle - React, Tailwind, and code Playground

HTML

<html>
  <head>
  </head>
  <body>
	<div id="appcontainer">
		If this container is larger than the window, a white area appears, and scrolling does not show this full container.
	</div>
  </body>
</html>

CSS

html { 
    height: 100%;
    margin:0px;
    background: url(../images/main_bg.png) no-repeat center center;
    background-size: cover;
}  
body { 
    min-height: 100%;
    margin:0px;
    
}
#appcontainer {
	position: absolute;
    background-color: rgba(255,255,255,0.7);
    width:960px; height:720px;
   	left:20px;
   	top:20px;
}