Background
Convey meaning through background-color and add decoration with gradients.
Bootstrap documentation.bg-primary
.bg-primary-subtle
.bg-secondary
.bg-secondary-subtle
.bg-success
.bg-success-subtle
.bg-danger
.bg-danger-subtle
.bg-warning
.bg-warning-subtle
.bg-info
.bg-info-subtle
.bg-light
.bg-light-subtle
.bg-dark
.bg-dark-subtle
.bg-body-secondary
.bg-body-tertiary
.bg-body
.bg-black
.bg-white
.bg-transparent
Background gradients
By adding a .bg-gradient
.bg-primary.bg-gradient
.bg-secondary.bg-gradient
.bg-success.bg-gradient
.bg-danger.bg-gradient
.bg-warning.bg-gradient
.bg-info.bg-gradient
.bg-light.bg-gradient
.bg-dark.bg-gradient
.bg-black.bg-gradient