feat(web): add smooth theme transition animation

apps/web/src/components/Navbar.css

@@ -34,7 +34,9 @@
   align-items: center;
   justify-content: center;
   font-size: 1.25rem;
-  transition: transform 0.24s ease, background-color 0.24s ease, border-color 0.24s ease;
+ transition: transform 0.24s ease, background-color 0.24s ease, border-color 0.24s ease;
+  overflow: hidden;
+  position: relative;
 }
 
 .theme-toggle:hover {
@@ -43,11 +45,36 @@
   border-color: rgba(99, 102, 241, 0.3);
 }
 
+.theme-toggle:active {
+  transform: scale(0.92);
+  background: rgba(99, 102, 241, 0.15);
+  border-color: rgba(99, 102, 241, 0.5);
+}
+
+.theme-toggle.glow {
+  animation: toggle-glow 0.5s cubic-bezier(0.4, 0, 0.2, 1) forwards;
+}
+
 .theme-toggle:focus-visible {
   outline: 3px solid rgba(99, 102, 241, 0.24);
   outline-offset: 3px;
 }
 
+.theme-toggle-icon {
+  display: inline-flex;
+  align-items: center;
+  justify-content: center;
+  line-height: 1;
+}
+
+.theme-toggle-icon.hiding {
+  animation: icon-hide 0.2s cubic-bezier(0.4, 0, 1, 1) forwards;
+}
+
+.theme-toggle-icon.showing {
+  animation: icon-show 0.25s cubic-bezier(0.34, 1.56, 0.64, 1) forwards;
+}
+
 @media (max-width: 860px) {
   .navbar {
     margin-top: 0.9rem;

apps/web/src/components/Navbar.tsx

@@ -1,9 +1,31 @@
+import { useState } from 'react';
 import { Link } from 'react-router-dom';
 import { useTheme } from '../lib/theme';
 import './Navbar.css';
 
+type IconState = 'idle' | 'hiding' | 'showing';
+
 export default function Navbar() {
   const { theme, toggleTheme } = useTheme();
+  const [iconState, setIconState] = useState<IconState>('idle');
+  const [displayedTheme, setDisplayedTheme] = useState(theme);
+  const [glowing, setGlowing] = useState(false);
+
+  const handleToggle = () => {
+    if (iconState !== 'idle') return;
+    setIconState('hiding');
+    setGlowing(true);
+  };
+
+  const handleAnimationEnd = () => {
+    if (iconState === 'hiding') {
+      toggleTheme();
+      setDisplayedTheme((t) => (t === 'dark' ? 'light' : 'dark'));
+      setIconState('showing');
+    } else if (iconState === 'showing') {
+      setIconState('idle');
+    }
+  };
 
   return (
     <nav className="navbar glass" id="main-nav">
@@ -13,14 +35,23 @@ export default function Navbar() {
           <span className="gradient-text">DevCard</span>
         </Link>
         <button
-          className="theme-toggle"
-          onClick={toggleTheme}
+          className={`theme-toggle${glowing ? ' glow' : ''}`}
+          onClick={handleToggle}
+          onAnimationEnd={(e) => {
+            if (e.animationName === 'toggle-glow') setGlowing(false);
+          }}
           aria-label={`Switch to ${theme === 'dark' ? 'light' : 'dark'} mode`}
           id="theme-toggle-btn"
         >
-          {theme === 'dark' ? '☀️' : '🌙'}
+          <span
+            className={`theme-toggle-icon ${iconState !== 'idle' ? iconState : ''}`}
+            onAnimationEnd={handleAnimationEnd}
+            aria-hidden="true"
+          >
+            {displayedTheme === 'dark' ? '☀️' : '🌙'}
+          </span>
         </button>
       </div>
     </nav>
   );
-}
+}

apps/web/src/index.css

@@ -56,6 +56,36 @@ html.dark {
   box-sizing: border-box;
 }
 
+
+html.theme-transitioning *,
+html.theme-transitioning *::before,
+html.theme-transitioning *::after {
+  transition:
+    background-color 0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    background       0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    color            0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    border-color     0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    box-shadow       0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    fill             0.35s cubic-bezier(0.4, 0, 0.2, 1),
+    stroke           0.35s cubic-bezier(0.4, 0, 0.2, 1) !important;
+}
+
+
+@keyframes icon-hide {
+  0%   { transform: scale(1)    rotate(0deg);   opacity: 1; }
+  100% { transform: scale(0)    rotate(-90deg); opacity: 0; }
+}
+
+@keyframes icon-show {
+  0%   { transform: scale(0)    rotate(90deg);  opacity: 0; }
+  100% { transform: scale(1)    rotate(0deg);   opacity: 1; }
+}
+@keyframes toggle-glow {
+  0%   { box-shadow: 0 0 0 0 rgba(99, 102, 241, 0.55); }
+  50%  { box-shadow: 0 0 0 8px rgba(99, 102, 241, 0.18); }
+  100% { box-shadow: 0 0 0 14px rgba(99, 102, 241, 0); }
+}
+
 body {
   font-family: 'Inter', sans-serif;
   background:
@@ -191,7 +221,10 @@ html {
 }
 
 @media (prefers-reduced-motion: reduce) {
-  * {
+  *,
+  html.theme-transitioning *,
+  html.theme-transitioning *::before,
+  html.theme-transitioning *::after {
     animation-duration: 0.01ms !important;
     animation-iteration-count: 1 !important;
     transition-duration: 0.01ms !important;

apps/web/src/lib/theme.tsx

@@ -31,7 +31,14 @@
     localStorage.setItem('devcard-theme', theme);
   }, [theme]);
 
-  const toggleTheme = () => setTheme((t) => (t === 'dark' ? 'light' : 'dark'));
+const toggleTheme = () => {
+  const root = document.documentElement;
+  root.classList.add('theme-transitioning');
+  const cleanup = () => root.classList.remove('theme-transitioning');
+  window.setTimeout(cleanup, 400);
+  root.addEventListener('transitionend', cleanup, { once: true });
+  setTheme((t) => (t === 'dark' ? 'light' : 'dark'));
+};
 
   return (
     <ThemeContext.Provider value={{ theme, toggleTheme }}>
@@ -40,7 +47,7 @@
   );
 }
 
 export function useTheme(): ThemeContextValue {
   const ctx = useContext(ThemeContext);
   if (!ctx) throw new Error('useTheme must be used within ThemeProvider');
   return ctx;