aspects.css

// Aspect ratio classes are useful for things like fluid-width background images
// These fill the width of parent elements

.aspect-square {
  width: 100%;
  height: 0;
  padding-bottom: 100%;  
}

.aspect-4o3 {
  width: 100%;
  height: 0;
  padding-bottom: 75%;
}

.aspect-16o9 {
  width: 100%;
  height: 0;
  padding-bottom: 56.25%;
}