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feat: smoother theme transition for dark mode switch #322

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Merged
greatest0fallt1me merged 1 commit into from
Jun 29, 2026
+42 −0
Merged

feat: smoother theme transition for dark mode switch #322

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11 changes: 11 additions & 0 deletions src/ThemeContext.tsx
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Original file line number Diff line number Diff line change
@@ -1,4 +1,5 @@
import React, { createContext, useContext, useEffect, useState } from 'react';
import './styles/theme-transition.css';

type Theme = 'light' | 'dark' | 'system';

Expand All @@ -22,6 +23,16 @@ export function ThemeProvider({ children }: { children: React.ReactNode }) {
return (resolvedTheme === 'light' || resolvedTheme === 'dark') ? resolvedTheme : 'dark';
});

// Enable color-token transitions only after the first paint, so the initial
// theme is applied instantly (no flash) while subsequent switches animate.
useEffect(() => {
const root = window.document.documentElement;
const id = window.requestAnimationFrame(() => {
root.classList.add('theme-transitions-ready');
});
return () => window.cancelAnimationFrame(id);
}, []);

useEffect(() => {
localStorage.setItem('callora-theme', theme);

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31 changes: 31 additions & 0 deletions src/styles/theme-transition.css
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Original file line number Diff line number Diff line change
@@ -0,0 +1,31 @@
/**
* theme-transition.css
*
* Smooth the light <-> dark theme switch by animating the color tokens
* (background, text and border colors) instead of swapping them instantly.
*
* The transition is only active once the ThemeProvider has mounted and added
* the `theme-transitions-ready` class to <html>. This prevents the colors from
* animating on the very first paint (which would otherwise look like a flash
* of the wrong theme fading in).
*/

html.theme-transitions-ready,
html.theme-transitions-ready body,
html.theme-transitions-ready *:not(.no-theme-transition) {
transition:
background-color var(--transition-speed, 240ms) ease,
border-color var(--transition-speed, 240ms) ease,
color var(--transition-speed, 240ms) ease,
fill var(--transition-speed, 240ms) ease,
stroke var(--transition-speed, 240ms) ease;
}

/* Respect users who prefer reduced motion: switch instantly. */
@media (prefers-reduced-motion: reduce) {
html.theme-transitions-ready,
html.theme-transitions-ready body,
html.theme-transitions-ready * {
transition: none !important;
}
}