New Theme Inversion

[j-mie6]

Some people were unapply with the sheer in-your-face redness of the new theme introduced in #573, so this just inverts the primary and secondary colours, creating a bit better of a balance. With this, the lighter red is brought back, which is a bit more soft (but had bad contrast at the small sizes on the nav-bar), and the landing page changes from #586 have been incorporated.

However, the landing page in Laika is not particularly well set-up for light backgrounds, so while we wait for that to be properly decoupled (text colour-wise), there is an interim darker landing page (note the button colour on that screenshot has since been altered):

Obviously, there is no default landing page for SBT typelevel currently, but this means the theme is currently a bit more future proofed. Eventually, the landing page will be lightened and all will be well with the world.

[j-mie6]

With the merging of #594 the interim dark landing colours have been removed in favour of:

[jenshalm]

A few fairly minor things I noticed for the normal content pages:

• The primaryMedium used for borders and lines is very light and barely visible. If you want to keep this tint for the landing page gradient, you could create one that is a tad darker for the normal pages.

• Literals in syntax highlighting are very dark, I find them hard to read. Even if it's temporary I think it would be good to make it a bit brighter.

• The background for code blocks is similar, but different to primary. It might look more harmonic if you use primary as syntax-bg, too

And I think it would be nice to remove unused/commented colors.

[j-mie6]

Addressed some of those (kept code background the same, as it is the colour for the TL logo's font and the main text colour:

(Also removed some unneeded colours, but kept redTl just in case)

[jenshalm]

Looks good to me now.