body {
    margin:0px;
    padding:0px
}
#app {
    background-image: url(hintergrundbild.jpeg);
    background-position: center center;
    background-size: cover;
    width: 100%;
    height:100vh;
}
video{
    position: absolute;
    width: 100%;
    height:100vh;
    display: none;
}
#button-container{
    position: absolute;
    bottom: 50px;
    left: 550px;
}
#button-container > button:first-child {
    background-color: yellow;
}
#button-container > button:nth-child(2) {
    background-color: blue;
}
#button-container > button:nth-child(3) {
    background-color: red;
}
#button-container > button:nth-child(4) {
    background-color: green;
}