Use brighness for links, opacity for monochrome icons.

[isoos]

• Opacity change on hover may not be a good idea #8493
• Setting the filter: brightness(...%) is much better for our links, as their color is now pushed towards stronger contrast.
• However, it does not work with the monochrome icons, introducing a new class for it and using it on the version's tab icons.

Hovering on the versions tab icons before:

Hovering on the versions tab icons after:

Note: the difference is that the current behavior reduced the contrast, while the new one increases it. It can also be tested on staging now.

[isoos]

/cc @parlough