Fix: overflow and adjust background image colors

[ryuash]

Description

Closes #39

Checklist

• [x] Targeted PR against correct branch.
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• [x] Wrote unit tests.
• [x] Updated the documentation.
• [x] Added an entry to the CHANGELOG.md file.
• [x] Re-reviewed Files changed in the Github PR explorer.

[codecov[bot]]

Codecov Report

Merging #40 into master will decrease coverage by 0.01%. The diff coverage is 6.12%.

@@            Coverage Diff             @@
##           master      #40      +/-   ##
==========================================
- Coverage   18.02%   18.01%   -0.02%     
==========================================
  Files         245      245              
  Lines        5958     5967       +9     
==========================================
+ Hits         1074     1075       +1     
- Misses       4884     4892       +8     

Impacted Files	Coverage Δ
.../notifications/remote/notifications_converter.dart	0.00% <ø> (ø)
lib/ui/localization/export.dart	0.00% <0.00%> (ø)
lib/ui/theme/decorations.dart	0.00% <0.00%> (ø)
lib/ui/widgets/buttons/primary_light_button.dart	0.00% <0.00%> (ø)
lib/ui/widgets/buttons/secondary_button.dart	0.00% <0.00%> (ø)
lib/ui/widgets/login/login_main_content.dart	0.00% <0.00%> (ø)
lib/ui/widgets/login/login_terms_conditions.dart	0.00% <0.00%> (ø)
...b/ui/widgets/post_actions/post_action_comment.dart	0.00% <0.00%> (ø)
lib/ui/widgets/post_actions/post_action_like.dart	0.00% <0.00%> (ø)
lib/utils/dependency_injector.dart	0.00% <0.00%> (ø)
... and 2 more

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