Update to support high contrast

[apple502j]

No description provided.

[Kenny2github]

I also have an alternative suggestion to my various comments about the code: Change it to hc-3 instead of 3-hc. That changes these selectors:

pre[class^=blocks-3-hc], pre[class^=blocks-3.0-hc] { /* ... */ }
pre[class^=blocks-3]:not([class$=-hc]) { /* ... */ }
/* and the same for <code> */

To these selectors:

pre[class^=blocks-hc-3] { /* ... */ }
pre[class^=blocks-3] { /* ... */ }