based from the answer of @SW4, you could also add a little animation at the end.
body > div{_x000D_
border:1px solid grey;_x000D_
}_x000D_
html, body, #container {_x000D_
height:100%;_x000D_
width:100%;_x000D_
margin:0;_x000D_
padding:0;_x000D_
}_x000D_
#container {_x000D_
overflow:hidden;_x000D_
position:relative;_x000D_
}_x000D_
#hideMe {_x000D_
-webkit-animation: cssAnimation 5s forwards; _x000D_
animation: cssAnimation 5s forwards;_x000D_
}_x000D_
@keyframes cssAnimation {_x000D_
0% {opacity: 1;}_x000D_
90% {opacity: 1;}_x000D_
100% {opacity: 0;}_x000D_
}_x000D_
@-webkit-keyframes cssAnimation {_x000D_
0% {opacity: 1;}_x000D_
90% {opacity: 1;}_x000D_
100% {opacity: 0;}_x000D_
}
_x000D_
<div>_x000D_
<div id='container'>_x000D_
<div id='hideMe'>Wait for it...</div>_x000D_
</div>_x000D_
</div>
_x000D_
Making the remaining 0.5 seconds to animate the opacity attribute. Just make sure to do the math if you're changing the length, in this case, 90% of 5 seconds leaves us 0.5 seconds to animate the opacity.