this adds the functions necessary for the other modes as well
BREAKING CHANGE:
Can now pass contrast to the colors map:
```
$colors-ios: (
primary: (
base: #327eff,
contrast: yellow
),
secondary: (
base: #32db64,
contrast: hotpink
),
danger: #d91e18,
light: #f4f4f4,
dark: #222
) !default;
```
references #5445
BREAKING CHANGE:
`$item-ios-divider-bg` is now `$item-ios-divider-background`
`$item-ios-sliding-content-bg` is now
`$item-ios-sliding-content-background`
`$item-md-divider-bg` is now `$item-md-divider-background`
`$item-md-sliding-content-bg` is now
`$item-md-sliding-content-background`
`$item-wp-divider-bg` is now `$item-wp-divider-background`
`$item-wp-sliding-content-bg` is now
`$item-wp-sliding-content-background`
references #5651
