crude initial adwaita > HC port
HC: flat OSD
HC: fix borders
HC: contrasty buttons
HC: sync dualogs with Adwaita
HC: thick button strokes
HC: selectable list items (sync with Adwaita)
HC: checkboxes and radios
Merge branch 'wip/hc-sass'

- Share style elements with Adwaita
- Keep similar structure as Adwaita