Minor UI changes for item detail toast and learn more link colors

[devinreams]

Fixes #267

Also starts but doesn't finish #262 - I just wanted to get sane colors in place for testing/usability, will wait to see what the final view/result built at #232 ends up so we can easily re-use

Testing and Review Notes

• open app
• open item detail
• observe the background color of the text link at the bottom matches the screen (grey, not white)
• tap copy button on username/password, observe the white on grey colors of the toast

Screenshots or Videos

To Do

• add “WIP” to the PR title if pushing up but not complete nor ready for review
• double check the original issue to confirm it is fully satisfied
• add testing notes and screenshots in PR description to help guide reviewers
• add unit tests
• consider running this branch in a debug simulator and check for memory leak notifications or any warnings
• request the "UX" team perform a design review (if/when applicable)
• make sure CI builds are passing (e.g.: fix lint and other errors)
• check on the accessibility of any added UI

[sashei]

lgtm; I'm sure you'll want a design review as well :)

[devinreams]

Waiting to merge after #232 is closed and a successful rebase/merge from master is completed...