fill div with 2 colors?

I ended up with this solution using linear gradients:

    .dualcol-test {
        background: linear-gradient(to right, green 0%, green 80%, red 80%, red 100%);
    }

   <div class="dualcol-test"> This div has a green and red background <br><br><br> </div>

You can't set multiple background colors, but you could set something like:

div.twocolorish {
    background-color: green;
    border-left: 20px solid red;
}

As long as you don't need text to go over the part in red then this would take care of you in one div.