html {
  font-size: 10px;
}

#central {
  width: 30rem;
  height: 30rem;
  background-image: radial-gradient(circle, white, blue, black);
  background-repeat: no-repeat;
  background-position: center center;
  background-size: cover;
/*  background-clip: border-box;*/
  border-radius: 100%;
  
}

a {
  font-size: 2rem;
}
a:hover, a:focus {
  outline: 15px solid black;
}