body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    text-align: center;

}
#Hours {
    width: 100px;
    margin: auto;
}
#Minutes{
    width: 100px;
    margin: auto;
}
#Seconds{
    width: 100px;
    margin: auto;
}
#start {
    width: 100px;
    margin: auto;
}
#stop {
    width: 100px;
    margin: auto;
}
.clock {
    font-size: 50px;
    width: 300px;
    font-family: 'Franklin Gothic Medium', 'Arial Narrow', Arial, sans-serif;
    color: white;
    text-align: center;
    margin: auto;
    background-color: white;
    position: relative;
    animation-name: Celebration;
    animation-duration: 4s;
    animation-iteration-count: 2;
    animation-direction: alternate-reverse; 
}
@keyframes Celebration {
    0%   {background-color:red; left:0px; top:0px;}
    25%  {background-color:yellow; left:200px; top:0px;}
    50%  {background-color:blue; left:200px; top:200px;}
    75%  {background-color:green; left:0px; top:200px;}
    100% {background-color:white; left:0px; top:0px;}
}