Button CSS fixes

[shawnbot]

• [x] Buttons with disappearing bottom borders:

  

• [x] Blocked by https://github.com/SFDigitalServices/sfgov/pull/948

[github-actions[bot]]

Size Change: -63 B (0%)

Total Size: 88.1 kB

Filename	Size	Change
dist/formio-sfds.css	14 kB	-35 B (0%)
dist/formio-sfds.standalone.js	67.7 kB	-28 B (0%)

ℹ️ View Unchanged

| Filename | Size | | :--- | :---: | | `dist/portal.js` | 6.37 kB |

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