h1 {color:blue;}
#container {
  position: absolute;
  top: 0;
  left: 0;
  width: 100vw;
  height: 100vh;
  margin:0;
  display:flex;
  justify-content:center;
  align-items:center;
}
#content{
  width:500px;
  height:500px;
  border:5px solid blue;
}
#content{
  width:500px;
  height:500px;
  border:5px solid blue;
  border-radius:50%;
}
#content{
  width:500px;
  height:750px;
  border:5px solid blue;
  border-radius:50%;
  overflow: hidden;
}
#content{
  width:1000px;
  height:500px;
  border:5px solid purple;
  border-radius:75%;
  overflow: hidden;
  background-image:url('https://th.bing.com/th/id/OIP.bmFFrDULN8_ShFG1VqXh5QHaEx?w=311&h=200&c=7&r=0&o=5&pid=1.7');
}