default.css

* {
    box-sizing: border-box;
    height: 100%;
}

body {
    margin: 0;
    height: 100%;
    overflow: hidden;
}

#header-wrapper , #footer-wrapper {
    margin: 0;
    width: 100%;
    height: 13%;
    display: table;
    background-color: #323030;
}

#main-wrapper {
    height: 76%;
    width: 100%;
    background-image: url("./bg/bg-ground.jpg");
    background-repeat: no-repeat;
    background-size: cover;
    padding: 2%;
}

.test-button {
    height: 20px;
    margin: 0 auto;
    text-align: center;
}

.icon {
    height: 35%;
}

#header-wrapper h1 {
    margin: 0;
    text-align: center;
    line-height: inherit;
    vertical-align: middle;
    font-family: 'Alfa Slab One';
    display: table-cell;
    color: ivory;
    letter-spacing: 0.1em;
}

#footer-wrapper h3 {
    margin: 0;
    line-height: inherit;
    vertical-align: middle;
    text-align: center;
    display: table-cell;
    color:#7b7a7a;
}

#start-button {
    height: 100%;
    width: 2em;
    line-height: inherit;
    color: ivory;
    vertical-align: middle;
    display: table-cell;
    margin: 0;
    text-align: right;
    padding-right: 1em;
    padding-top: 1em;
    font-size: 2em;
}