.header {
    font-size: 36px;
    justify-content: center;
    display: flex;
    background: #ccc;
}

.menu-and-content {
    display: flex;
}

.menu {
    width: 150px;
    padding: 10px;
    background: #c9cc00;
    min-height: 300px;
}

    .menu .link {
        border: red 1px solid;
        border-radius: 5px;
        margin: 3px;
    }