styles.css

html {
    height: 100%;
    width: 100%;
    margin: 0;
}
body {
    background-color: #212121;
    height: 100%;
    width: 100%;
    margin: 0;
}
viewport {
    height: 100%;
    width: 100%;
    margin: 0;
}

#container {
    height: 100%;
    display: -webkit-flex;
    display:    -moz-flex;
    display:         flex;
    -webkit-flex-direction: column;
    -moz-flex-direction:    column;
    flex-direction:         column;
    -webkit-justify-content: center;
    -moz-justify-content:    center;
    justify-content:         center;
    -webkit-align-items: center;
    -moz-align-items:    center;
    align-items:         center;
}

#logo {
    height: 250px;
}

#buttons {
    margin-top: 5%;
    display: -webkit-flex;
    display:    -moz-flex;
    display:         flex;
    -webkit-flex-wrap: wrap;
    -moz-flex-wrap:    wrap;
    flex-wrap:         wrap;
    width:344px;
}

.button {
    margin: 8px;
    padding: 15px;
    padding-top: 12px;
    padding-bottom: 8px;
    background-color: #E0E0E0;
    -webkit-border-radius: 5px;
    -moz-border-radius:    5px;
    border-radius:         5px;
    -webkit-box-shadow: 1px 2px 2px #000;
    -moz-box-shadow:    1px 2px 2px #000;
    box-shadow:         1px 2px 2px #000;
    -webkit-transition: all .2s;
    -moz-transition:    all .2s;
    -o-transition:      all .2s;
    transition:         all .2s;
}

.button:hover {
    -webkit-box-shadow: 2px 4px 4px #000;
    -moz-box-shadow:    2px 4px 4px #000;
    box-shadow:         2px 4px 4px #000;
    margin-top:6px;
    margin-bottom:10px;
    background-color: #fff;
    -webkit-transition: all .2s;
    -moz-transition:    all .2s;
    -o-transition:      all .2s;
    transition:         all .2s;
}

.button img {
    height: 40px;
    width: 40px;
}