flexbox everything

border-layout.css

*, *:before, *:after {
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
}

* {
    position: relative;
}

html, body {
    font-size: 16px;
    line-height: 1.5rem;
    height: 100%;
    min-height: 100%;
    background: #ddd;
}

.border-layout {
    display: flex;
    flex: 1;
    position: relative;
}

.vertical {
    flex-direction: column;
    height: 100%;
    min-height: 100%;
}

.horizontal {
    flex-direction: row;
    height: 100%;
    position: absolute;
    left: 0;
    right: 0;
}

.vertical > .header {
    background: #E74C3C;
    height: 3rem;
    width: 100%;
}

.horizontal > .header {
    background: #27AE60;
    width: 3rem;
    height: 100%;
}

.vertical > .content {
    background: #2980B9;
}

.horizontal > .content {
    background: #95A5A6;
    height: 100%;
}

.content {
    flex: 1;
}