Minor fix: darker green on buttons and links

The green on our buttons and in-article links sat just below the contrast level that makes text comfortable to read — fine on a good screen, harder in daylight or with tired eyes.

It is now darker across the site, including the theme layer that paints buttons on every marketing page. A small correction, and invisible unless you needed it.

One rule came out of it: never two green buttons side by side. If everything is the primary action, nothing is.