Each theme value can be default or custom value.

The function which uses 'Default' value should know how to evaluate or set the default value.

Helper function to determine the given value is an Default value

It works similar to Maybe.withDefault

Helps to set a value to some variable or field with default value if user does not supply any custom value.

        fontSize
            = Theme.withDefault defaultFontSize theme.fontSize

or

        fontSize
            = theme.fontSize
            |> Theme.withDefault defaultFontSize

depends on your preference.

Recommened Palette type is PaletteWith Color

default palette for defaultTheme and viewElement

Just an example of light palette

lightPalette : Palette
lightPalette
    = let
        lowContrast -- lowContrast to `light' : dark colour
            = Color.rgb255 0xE7 0xE0 0xD0
        highContrast
            = Color.rgb255 0x14 0x11 0x11

   in
       { primary
             = Color.rgb255 0x3D 0x5A 0x75
       , secondary
             = Color.rgb255 0x82 0x8C 0x74
       , success
             = Color.rgb255 0x74 0xAC 0x88
       , info
             = Color.rgb255 0x7F 0xAE 0xE2
       , warning
             = Color.rgb255 0xFC 0xC3 0x5C
       , danger
             = Color.rgb255 0xB5 0x05 0x46
       , accent
             = Color.rgb255 0x05 0x45 0x76
       , surface
             = lowContrast
       , background
             = Color.rgb255 0xEC 0xFB 0xED

      , on = { primary
                   = lowContrast
             , secondary
                   = highContrast
             , success
                   = lowContrast
             , info
                   = highContrast
             , warning
                   = lowContrast
             , danger
                   = lowContrast
             , accent
                   = lowContrast
             , surface
                   = highContrast
             , background
                   = lowContrast
             }
       , toElmUiColor
           = ColorUtil.toElmUiColor
      }