body {
    background-color: lightgray;
}

/* Spacers */
.spacer-xs { height: 0.25rem; }  /* 4px */
.spacer-sm { height: 0.5rem; }   /* 8px */
.spacer-md { height: 1rem; }     /* 16px */
.spacer-lg { height: 2rem; }     /* 32px */
.spacer-xl { height: 4rem; }     /* 64px */