@keyframes changeBackground {
  0% { background-image: url(dark.jpg); background-size: cover;  }
  35% { background-image: url(milk.jpg); background-size: cover; }
  65% { background-image: url(black.jpg); background-size: cover; }
  100% { background-image: url(blue.jpg); background-size: cover; }
}

body {
animation: changeBackground 25s infinite; 
min-height: 100vh;
display: flex;
margin: 0;
}


/*
html, body {
min-height: 100vh;
display: flex;
margin: 0;
background-image: url(dark.jpg);
background-size: cover;                    
background-repeat: no-repeat;
background-position: center center;
}*/

.zentriert {
background-color: #FFFFFF;
width: 800px;
position: absolute;
top: 50%;
left: 50%;
transform: translate(-50%, -50%);
border: 5px solid #364048;
/*border-radius:2em;*/
box-shadow: 20px 20px 30px silver;
}

.frontfont {
font-family: verdana,arial,helvetica,sans-serif,sans;
font-size: 15pt;
text-shadow: 2px 2px 3px rgba(150, 150, 150, 1);
color: #00004F;
}

.font {
font-family: verdana,arial,helvetica,sans-serif,sans;
font-size: 15pt;
text-shadow: 2px 2px 3px rgba(150, 150, 150, 1);
color: #5A545E;
}

.td_links {
background-image: url(small.jpg);
background-size: cover;                   
background-repeat: no-repeat;
background-position: center center;
margin: 0px;
}

.logo {
display: block;
margin-top: 15px;
margin-left: 20px;
opacity: 1.0;
}