Check out the solution below:
To make the image cover the entire screen, use background-size: 100% 100%;
For a responsive h1 that adjusts to different screen sizes, check out the code snippet below:
html {
height: 100%;
}
body {
color: #EEEEEE;
font: 24px/1.3 "arial";
min-height: 100%;
background: url("http://media.giphy.com/media/13bGgH9VnEDsuA/giphy.gif") no-repeat scroll 0 0 / 100% 100% #000000;
height: auto;
margin: 0;
width: 100%;
}
h1 {
color: #F0F0F0;
font-family: "belta bold";
font-size: 212px;
left: 0;
margin: -120px 0 0;
position: absolute;
text-align: center;
top: 50%;
width: 100%;
}
For a more precise solution, utilize CSS media queries as shown in the following fiddle: http://jsfiddle.net/krunalp1993/53zaT/
Make your h1 responsive by using media queries like this:
@media screen and (max-width:1024px){
h1{
font-size:62px;
margin-top:-31px;
}
}
Here is the updated fiddle with media queries applied: http://jsfiddle.net/krunalp1993/53zaT/2/
I hope this information helps you :)