jmak

=triangle($direction: right, $size: 10px, $color: #999)
  width: 0
  height: 0
  line-height: 0
  border: $size solid transparent
  @if $direction == top
    border-bottom-color: $color
  @else if $direction == right
    border-left-color: $color
  @else if $direction == bottom

jmak

iOS, OS X Spinner

A Pen by Maciej Jarczok on CodePen.

License.

jmak

What forces layout / reflow

All of the below properties or methods, when requested/called in JavaScript, will trigger the browser to synchronously calculate the style and layout*. This is also called reflow or layout thrashing, and is common performance bottleneck.

Element

Box metrics

• elem.offsetLeft, elem.offsetTop, elem.offsetWidth, elem.offsetHeight, elem.offsetParent
• elem.clientLeft, elem.clientTop, elem.clientWidth, elem.clientHeight
• elem.getClientRects(), elem.getBoundingClientRect()

jmak

Similar to the media toggle approach, we could also load CSS asynchronously by marking a link as an alternate stylesheet (designed to offer the user alternate presentations of a site), and then using JavaScript to toggle the rel attribute back to stylesheet when the file loads:
<link rel="preload" href="mystyles.css" as="style" onload="this.rel='stylesheet'">