xxx is one of the following values:
An alternate set of values that could be used are:
- tint (same as lighter)
- background (same as light)
- border (same as dark)
If xxx is not specified, the default value is light, although leaving it as the default is discouraged.
Aside from special circumstances, always attempt to use the more appropriate set of color values - either lighter-light-dark or tint-background-border. Avoid mixing them up.