!base_color        ||= red
!dark_base_color     = darken(!base_color, 25)
!darker_base_color   = darken(!base_color, 50)
!darkest_base_color  = darken(!base_color, 75)
!light_base_color    = lighten(!base_color, 25)
!lighter_base_color  = lighten(!base_color, 75)
!lightest_base_color = lighten(!base_color, 50)