JSFiddle - React, Tailwind, and code Playground by Suryar Praveen June 07, 2023 HTML <header>Some nav stuff here</header> <h1>This is the heading</h1> <div id="theCalcDiv">This blocks needs to have a CSS calc() height of 100% - the height of the other elements.</div> CSS html,body { background: blue; height:100%; padding:0; margin:0; } header { background: red; height: 20px; width:100% } h1 { font-size:1.2em; margin:0; padding:0; height: 30px; font-weight: bold; background:yellow } #theCalcDiv { background:green; height: -moz-calc(100% - (20px + 100px)); height: -webkit-calc(100% - (20px + 100px)); height: calc(100% - (20px + 100px)); display:block }