Accessibility issues due to theme colors

[chalin]

See next for a sampling of Docsy alerts as they appear now. Notice:

• The poor contrast
• The poor differentiation of colors across different color classes: secondary, danger, and warning look all the same.

Contrast this with the Bootstrap defaults:

Docsy needs a better base color theme, even if this means just falling back to the Bootstrap default.

Related:

• Docsy/User-guide "skin" styles should be factored out and/or dropped in some cases #1655