footer {
    position: absolute;
    display: block;
    bottom: 0px;
    width: 100%;
}

h1 {
    margin-top: 25%;
}

.button {
    display: inline-block;
    width: calc(100% - 20px);
    margin: 5px;
    line-height: 50px;
    font-size: 125%;
}