Split Div Into 2 Columns Using CSS

Question

I have been attempting to split a div into two columns using CSS, but I have not managed to get it working yet. My basic structure is as follows:

Answer 1

Make children divs inline-block and they will position side by side:

#content {
   width: 500px;
   height: 500px;
}

#left, #right {
    display: inline-block;
    width: 45%;
    height: 100%;
}

See Demo