body {
  background-color: powderblue;
}
  body {
  background-image: url('https://i.pinimg.com/1200x/af/59/2a/af592a8e30424e9a96024051bdbbae46.jpg');
  background-repeat: no-repeat;
  background-attachment: fixed;
  background-size: cover;
  padding: 40px;
    display: flex; justify-content: center;
}

 .container:before, .container:after {
    display:table;
    content:"";
    zoom:1 /* ie fix */;
}

.container:after {
    clear:both;
}

.container {
  background: linear-gradient(to bottom, #ffffff 0%, #73DCFF 100%);
    width:800px;
    border:5px solid #00B4F6;
    border-radius:25px;
    background-color:#ffffff;
   display: flex; flex-direction: column; overflow: hidden;
}

.mainbody {
    height:800px;
    width:500px;
    border: solid #eee;
    border-width:0px ;
}


.header {
  height: 125px;
  background-image: url(https://files.catbox.moe/aheqf1.jpg);
  background-size: cover;
  background-position: center;
  border-bottom: 5px solid #00B4F6
}