Main button colour: five new options

None of the first five looked good, so here are five more, F to J. Each one is shown at a lesson end, on the sign-in page and at phone width, with rest, hover and keyboard focus. Every label in F to J passes 4.5 to 1 in all three states. The earlier A to E are further down, unchanged. Nothing else changes until you pick.

New options

Earlier options (none picked)