I've tried quite a few variants with no luck. What am I missing?
#menu {
 position: absolute;
 width: 50px;
 height: 250px;
 top: 15px;
 left: 0;
 background-color: #ee2e24;
 color: white;
}
#menu span {
 transform: rotate(90deg);
 transform-origin: left top 0;
}
<div id="menu"><span>MAIN MENU</span></div>