html, body {
    margin: 0;
    padding: 0;
}

.full-screen {
    width: 100vw;
    height: 100vh;
}

.full-screen-button {
    position: absolute;
    top: 5vh;
    left: calc(50vw - 3em);
    padding: .5em 1.25em;
    margin: auto;
    background: #54B555;
    border-radius: 5px;
    box-shadow: rgba(0,0,0,.5) 0 0 10px;
    font-size: 24px;
    color: #fff;
    transition: all .2s;
}