Simple single-element spinner using CSS3 animations

spinner.css

body {
  background-color: #d6e0e6;
}

.spinner {
  position: absolute;
  top: 50%;
  left: 50%;
  margin-left: -21.5px;
  margin-top: -21.5px;
  width: 40px;
  height: 40px;
  border-radius: 80px;
  border: 3px solid transparent;
  border-left-color: rgba(90, 126, 150, 0.2);
  border-right-color: rgba(90, 126, 150, 0.2);
  animation: spinnit 1s linear infinite;
}

.spinner:after {
  content: "";
  position: absolute;
  top: 2px;
  left: 2px;
  width: 30px;
  height: 30px;
  border-radius: 60px;
  border: 3px solid transparent;
  border-left-color: rgba(90, 126, 150, 0.5);
  border-right-color: rgba(90, 126, 150, 0.5);
  animation: spinnit 0.5s linear infinite reverse;
}

.spinner:before {
  content: "";
  position: absolute;
  top: 7px;
  left: 7px;
  width: 20px;
  height: 20px;
  border-radius: 40px;
  border: 3px solid transparent;
  border-left-color: rgba(90, 126, 150, 0.8);
  border-right-color: rgba(90, 126, 150, 0.8);
}

@keyframes spinnit {
  from {
    transform: rotate(0deg);
  }

  to {
    transform: rotate(360deg);
  }
}

spinner.html

<div class="spinner"></div>

spinner.scss

$outer-spinner-size:  40px;
$inner-spinner-size:  30px;
$center-spinner-size: 20px;
$border-width:        3px;
$core-spinner-color:  #5A7E96;

@mixin make-spinner($size, $border-opacity) {
	width: $size;
	height: $size;
	border-radius: $size * 2;
	border: $border-width solid transparent;
	border-left-color: rgba($core-spinner-color, $border-opacity);
	border-right-color: rgba($core-spinner-color, $border-opacity);  
}

@mixin offset-inner($inner-size) {
	$offset: ((($outer-spinner-size - $inner-size) / 2) - $border-width);
	top: $offset;
	left: $offset;
}

body {
	background-color: lighten($core-spinner-color, 40%);
}

.spinner {
	position: absolute;
	top: 50%;
	left: 50%;
	margin-left: -(($outer-spinner-size + $border-width) / 2);
	margin-top: -(($outer-spinner-size + $border-width) / 2);
	@include make-spinner($outer-spinner-size, 0.2);
	animation: spinnit 1s linear infinite;
}

.spinner:after {
	content: "";
	position: absolute;
	@include offset-inner($inner-spinner-size);
	@include make-spinner($inner-spinner-size, 0.5);
	animation: spinnit 0.5s linear infinite reverse;
}

.spinner:before {
	content: "";
	position: absolute;
	@include offset-inner($center-spinner-size);
	@include make-spinner($center-spinner-size, 0.8);
}

@keyframes spinnit {
	from { transform: rotate(0deg); }
	to { transform: rotate(360deg); }
}