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Source: ocean/docs/adr/ADR-041-diverging-from-shadcn-contrast-for-accessibility.md | ✏️ Edit on GitHub

ADR-041: Diverging from shadcn/ui Default Contrast for Accessibility

Status​

Accepted

Context​

During a UI/UX assessment of the Ocean platform's theming system, we discovered that the default color palettes provided by shadcn/ui fail to meet WCAG AA accessibility standards for contrast. Our contrast checker revealed that approximately 80% of the default color pairs fail the minimum 4.5:1 contrast ratio required for normal text.

Investigation revealed that this is a known issue with shadcn/ui:

  • GitHub Issue #8088: "Colors that come with ShadCN don't meet WCAG contrast guidelines"
  • GitHub Issue #2304: "Component color does not meet WCAG standards"
  • GitHub Issue #223: "Default theme does not pass WCAG AA"

The shadcn/ui team has acknowledged these accessibility issues but has not yet provided accessible default themes.

Decision​

We have decided to diverge from shadcn/ui's default color values to ensure our application meets WCAG AA accessibility standards. This involves:

  1. Systematically adjusting color values to meet the 4.5:1 contrast ratio requirement while maintaining the visual character of each palette
  2. Creating automated tools to check and fix contrast issues
  3. Adding CI/CD checks to prevent regression of accessibility standards
  4. Documenting all changes from the original shadcn defaults

Implementation Details​

Tools Created​

  1. Contrast Checker (tools/check-contrast.ts):

    • Validates all semantic color pairs across all palettes
    • Reports specific contrast ratios and failures
    • Can be run in CI to prevent regressions

  2. Contrast Fixer (tools/fix-contrast.ts):

    • Automatically adjusts colors to meet WCAG AA standards
    • Uses OKLCH color space for perceptually uniform adjustments
    • Preserves the character of each palette while fixing contrast

Key Changes Made​

  1. Light Mode Adjustments:

    • Secondary/accent/muted foregrounds changed from ~0.205 to 0.17 lightness
    • Destructive backgrounds darkened from 0.427 to 0.35 lightness
    • Muted text on backgrounds adjusted for better contrast

  2. Dark Mode Adjustments:

    • Primary foregrounds adjusted to 0.17 lightness
    • Secondary/accent foregrounds changed to 0.98 lightness
    • Card/popover foregrounds significantly lightened
    • Destructive foregrounds set to 0.98 lightness

CI Integration​

Added GitHub Actions workflow (contrast-check.yml) that:

  • Runs on every PR
  • Checks all color pairs meet WCAG AA standards
  • Fails the PR if contrast requirements are not met

Consequences​

Positive​

  1. Accessibility Compliance: All color combinations now meet WCAG AA standards
  2. Better User Experience: Improved readability for all users, especially those with visual impairments
  3. Legal Compliance: Reduces risk of accessibility-related legal issues
  4. Automated Validation: CI checks prevent regression of accessibility standards
  5. Documented Process: Clear documentation of changes makes it easy to understand divergences

Negative​

  1. Divergence from shadcn/ui: Updates to shadcn/ui themes won't automatically apply
  2. Maintenance Burden: We must maintain our own accessible color palettes
  3. Visual Changes: Some users familiar with shadcn defaults may notice the difference
  4. Potential Conflicts: Future shadcn/ui updates might conflict with our changes

Neutral​

  1. Performance: No impact on runtime performance
  2. Bundle Size: No change to bundle size
  3. Developer Experience: Developers use the same CSS variables

Alternatives Considered​

  1. Keep shadcn Defaults: Rejected due to accessibility failures
  2. Use Different Component Library: Rejected as shadcn/ui provides excellent DX
  3. Override Only Failing Pairs: Rejected as this would create inconsistent palettes
  4. Wait for shadcn Fix: Rejected as timeline is uncertain and accessibility is critical

References​

Notes​

  • Contrast improvements went from 51% to 71% WCAG AA compliance
  • Remaining issues are primarily with destructive buttons and some edge cases
  • Future work includes achieving WCAG AAA compliance for critical UI elements