Bootstrap includes several predefined button styles, each serving its own
semantic purpose, with a few extras thrown in for more control.
Using color to add meaning only provides a visual indication, which will
not be conveyed to users of assistive technologies – such as screen readers.
Ensure that information denoted by the color is either obvious from the
content itself (e.g. the visible text), or is included through alternative
means, such as additional text hidden with the .sr-only class.