how to center a footer div on a webpage

Center a div horizontally? Typically done by setting margin: 0 auto, or margin-left: auto; margin-right: auto.

And if you want a gap above it, give it a top margin.

#footer{
    display: table;
    text-align: center;
    margin-left: auto;
    margin-right: auto;
}

Use margin:auto to centre blocks with CSS, and margin-top or padding-top to make a gap above it:

#footer {
    margin-left:auto;
    margin-right:auto;
    margin-top:2em;
}

I've used 2em for the top margin; feel free to change that as you like, even to a fixed pixel size if you prefer. You can also use padding-top as well as or instead of margin-top, depending on exactly what you need to achieve, though the centering can only be done with margin left/right, not padding.

The above code can be condensed using the shorthand margin code, which lets you list them all in the same line of code:

#footer {
    margin: 2px auto 0 auto;
}

(sequence is top, right, bottom, left)

hope that helps.

I solved it with this:

#footer {
width: 100%;
height: 28px;
border-top: 1px solid #E0E0E0;
position: absolute;
bottom: 0px; 
left: 0px; 
text-align: center; 
}