Simple loader - https://jsfiddle.net/hewbt3qy/11/

loader.css

body {
  background: cyan;
}

@keyframes donut-spin {
  0% {
    transform: rotate(0deg);
  }
  100% {
    transform: rotate(360deg);
  }
}
.donut-container {
  position: absolute;
  display: flex;
  justify-content: center;
  align-items: center;
  width: 100%;
  height: 100%;
}
.donut {
  position: absolute;
  display: inline-block;
  border: 7px solid rgba(0, 0, 0, 0.1);
  border-left-color: #fff; 
  border-radius: 50%; 
  width: 50px;
  height: 50px;
  animation: donut-spin 1.2s linear infinite;
}

loader.html

<div class="donut-container">
  <div class="donut"></div>
</div>