How do I make the Decode theme responsive?

Stephen was a great help getting the issue resolved. I hope it helps someone else out there. I’m in WordPress Decode theme. This floats the bottom custom menu at the bottom (in the footer), turns its background white, and sets padding so the page text scrolls above it without going behind it. I set the height at 57 so mu menu buttons would show in mobile.

body {
    overflow: scroll;
}

#colophon {
    background: white;
    bottom: 0;
    font-size: 13px;
    height: 57px;
    position: fixed;
    padding: 0 30px;
    margin-bottom: 0;
    width: 100%;
}

.entry-content {
    padding-bottom: 30px;
}