100% height

HTML

<div id="navtower">Content for  id "navtower" Goes Here</div>
<div id="topbar">Content for  id "navtower" Goes Here</div>
<div id="maincontent">Content for  id "navtower" Goes Here
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content for  id "navtower" Goes Here<br/>
Content...

CSS

html, 
				body {
					margin:0;
					padding:0;
					height:100%;
				}
				body {
					position:relative;
				}
				#topbar {
					height: 40px;
					width: calc(100% - 200px);
					position: absolute;
					left: 200px;
					background-color: #CA0000;
					z-index:99;
				}
				#navtower {
					width: 200px;
					left: 0px;
					top: 0px;
					bottom: 0px;
					height:100%;
					background-color: #CA0000;
					position: absolute;
					z-index:99;
				}
				#maincontent {
					min-height: 100%;
					width: calc(100% - 200px);
					left: 200px;
					background-color: #E3E1FF;
					position: absolute;
					top: 40px;
				}