.loader {
  background:linear-gradient(yellow, #e90b5a);
  /* Show only 10px from the border */
  -webkit-mask:radial-gradient(farthest-side,transparent calc(100% - 10px),#fff 0);
          mask:radial-gradient(farthest-side,transparent calc(100% - 10px),#fff 0);
  width: 100px;
  height: 100px;
  border-radius: 50%;  
  position: fixed;
  top: calc(50% - 50px);
  left: calc(50% - 50px);  
  animation: rot 2s linear infinite; 
}

@keyframes rot {
   100% { transform: rotate(360deg); }
}

body {
  background:linear-gradient(to right,grey,white)
}