Dark Mode Done Right: Performance & Accessibility Considerations

Dark mode has become a standard feature in modern web design, offering a sleek aesthetic and potential benefits like reduced eye strain and energy savings. However, implementing dark mode goes beyond just inverting colors—it requires careful consideration of performance and accessibility to ensure an optimal user experience.

This guide explores the best practices for implementing dark mode effectively while balancing performance and accessibility.

Performance Considerations

Efficient Theme Switching

Avoid unnecessary re-renders or expensive computations when switching between light and dark themes.

Best Practices:

• Use CSS variables instead of toggling entire stylesheets.
• Leverage prefers-color-scheme to detect system settings and apply the preferred theme without JavaScript.
• Minimize DOM manipulation—apply class toggling at the highest parent container to reduce reflows and repaints.

:root {
  --bg-color: #ffffff;
  --text-color: #000000;
}

[data-theme="dark"] {
  --bg-color: #121212;
  --text-color: #ffffff;
}

body {
  background-color: var(--bg-color);
  color: var(--text-color);
}

Reduce Flash of Unstyled Content (FOUC)

If dark mode relies on JavaScript, users may experience a white flash before the theme applies.

Best Practices:

• Apply styles using CSS media queries instead of waiting for JavaScript execution.
• Store user preferences in localStorage and apply them before page load.
• Use a server-rendered default (e.g., SSR frameworks like Next.js can serve the preferred theme on the first request).

const userPref = localStorage.getItem("theme");
if (userPref) {
  document.documentElement.setAttribute("data-theme", userPref);
}

Optimizing Image and Video Assets

Dark mode can impact how images and videos appear, sometimes causing contrast issues.

Best Practices:

• Use picture elements with different images for dark and light modes.
• Convert transparent PNGs to WebP for better adaptability across themes.
• Adjust brightness and contrast dynamically for embedded media.

   srcset="dark-mode-image.jpg" media="(prefers-color-scheme: dark)">
   src="light-mode-image.jpg" alt="Adaptive image">

Accessibility Considerations

Ensuring Sufficient Contrast

Not all users perceive colors the same way. Poor contrast can make content unreadable.

Best Practices:

• Follow WCAG contrast ratio recommendations (minimum 4.5:1 for normal text, 3:1 for large text).
• Use tools like Contrast Checker or browser DevTools to test contrast.
• Avoid using pure black (#000000) on pure white (#ffffff), as high contrast can cause discomfort.

[data-theme="dark"] {
  --bg-color: #121212;
  --text-color: #E0E0E0; /* Softer than pure white */
}

Respecting User Preferences

Some users prefer light mode due to medical conditions like photophobia.

Best Practices:

• Default to prefers-color-scheme instead of forcing dark mode.
• Provide an easy toggle option with a persistent setting.
• Ensure dark mode does not remove essential visual cues (like borders or shadows).

Handling Motion & Animations

Animations in dark mode can be distracting, especially for users with vestibular disorders.

Best Practices:

• Respect prefers-reduced-motion for disabling unnecessary animations.
• Use subtle transitions instead of harsh flickers or sudden changes.
• Avoid blinking effects that can cause accessibility issues.

@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}

Conclusion

Implementing dark mode isn’t just about inverting colors—it’s about optimizing for performance and accessibility to create a seamless experience for all users. By using efficient theming, avoiding UI flashes, and considering contrast and accessibility needs, you can ensure that your dark mode implementation is both user-friendly and high-performing.