header {
    width: 100%;
    height: 4rem;

    position: fixed;
    left: 0;
    top: 0;

    background: #333;
    border-radius: 0 0 9px 9px;

    z-index: 1;
}

header button {
    width: 37%;
    height: 80%;

    position: absolute;
    right: 1%;
    top: 10%;

    font-size: 1.37rem;

    background: silver;
    color: #3498db;
    border: 1px solid #3498db;
    border-radius: 8px;

    cursor: pointer;
}

header button:hover {
    background: #3498db;
    color: silver;
    border: 1px solid silver;
}