html,
body {
    position: relative;
    width: 100%;
    height: 100%;
    margin: 0;
    padding: 0;
    overflow: hidden;
}

#main {
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    bottom: 0;
    margin: 0;
    padding: 0;
    overflow: hidden;
}

body.has-code {
    background: #eee;
}
.has-code #code-box {
    position: absolute;
    left: 0;
    top: 0;
    bottom: 0;
    width: 290px;
    margin: 0;
    border: 3px solid #aaa;
    overflow: auto;
}
.has-code #code-area {
    position: absolute;
    left: 0;
    padding: 10px;
    top: 0;
    bottom: 0;
    width: 500px;
}
.has-code #main {
    left: 300px;
    user-select: none;
    -webkit-user-select: none;
}