Removing space at the top left and right of div

Answer 1

You need to reset both the default padding and margin attributes in your stylesheet:

html, body {
    margin: 0;
    padding: 0;
}

As @Jason McCreary mentions, you should also look into using a reset stylesheet. The one he links to, Eric Meyer's CSS reset, is a great place to start.

It also looks like you're missing a semi-colon in your css, it should look as follows:

.top
{
    background-color:#3B5998;
    margin-left:0px;
    margin-top:0px;
}