body,
html,
div {
    padding: 0;
    margin: 0;
}
* {
    box-sizing: border-box;
    font-family: helvetica, arial, sans-serif;
}

button {
    margin: 0;
}
html {
    height: 100%;
}
body {
    background: #333 url(assets/images/wall.png) no-repeat center / cover;
    height: 100%;
}