.bkgd-dark

.bkgd-grey .bkgd-gray

.bkgd-light

Grid (40% opacity)

.bkgd-grid40 .bkgd-grid

Math (30% opacity)

.bkgd-grid30

Math (20% opacity)

.bkgd-grid20

Surround (10% opacity)

.bkgd-grid10 .bkgd-surround

Transparent

.bkgd-transparent