CSS to fit sidebar under topbar

Question

I need to create an empty topbar and an empty sidebar as below. I want to stack them neatly so that the top of the sidebar touches the bottom of the topbar. For that, I am using percentage. However, I just can't get them to do that.

I saw some other threads suggesting to set html and body with height: 100%; and width: 100% . But in my app, the layout below is not in the main html document.

 #nav-bar { position: absolute; top: 0; left: 0; background-color: blue; height: 10%; width: 100%; } #side-bar { position: absolute; top: 0; left: 0; background-color: #011a21; height: 90%; width: 7.5%; /*margin-top: 10%;*/ }

 <div id="nav-bar">&nbsp;</div> <div id="side-bar"></div>

Answer 1

I tend to use flex box for this, Maybe grid would be smarter though. I took also care of some scrolling things. Using min with and height 0 on flex parents is key for that.

 body, section { min-height: 0; min-width: 0; } body { padding: 0; margin: 0; display: flex; flex-direction: column; height: 100vh; } nav { height: 2rem; background: green; } section { flex: 1 1 0%; display: flex; } aside { width: 4rem; background: blue; height: 100%; } main { background: pink; flex: 1 1 0%; overflow: auto; padding: 1rem; } div { border: 1px black dashed; height: 300%; }

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Answer 2

Your #nav-bar has a height: 10% , and you can set the same value for the top rule, selector #side-bar .

 #nav-bar { position: absolute; top: 0; left: 0; background-color: blue; height: 10%; width: 100%; } #side-bar { position: absolute; top: 10%; left: 0; background-color: #011a21; height: 90%; width: 7.5%; /*margin-top: 10%;*/ }

 <div id="nav-bar">&nbsp;</div> <div id="side-bar"></div>