.wrapper {
    display: flex;
    flex-direction: column;
    height: 100vh;
}
header,
footer {
    height: 50px;
    background-color: #666;
}
.content {
    background-color: #ccc;
    flex: 1;
}
.columns {
    display: flex;
    height: 100%;
}
.main {
    flex: 1;
    background-color: #ccc;
}
.sidebar {
    width: 20%;
    background-color: #999;
}