You need to set the parent element to 100%
as well
html, body {
height: 100%;
}
Demo (Changed the background
for demo purpose)
Also, when you want to cover entire screen, seems like you want to dim
, so in this case, you need to use position: fixed;
#dimScreen {
width: 100%;
height: 100%;
background:rgba(255,255,255,0.5);
position: fixed;
top: 0;
left: 0;
z-index: 100; /* Just to keep it at the very top */
}
If that's the case, than you don't need html, body {height: 100%;}