feat(ui): add light and dark mode theme toggle

src/app/globals.css

 @import "tailwindcss";
 
+:root {
+  /* Default Dark Mode Values */
+  --primary: #3b82f6;
+  --primary-glow: rgba(59, 130, 246, 0.1);
+  --secondary: #8b5cf6;
+  --bg: #0b0f19;
+  --surface: #111827;
+  --surface-border: rgba(255, 255, 255, 0.05);
+  --surface-hover-border: rgba(255, 255, 255, 0.12);
+  --text-primary: #f9fafb;
+  --text-secondary: #94a3b8;
+  --nav-bg: rgba(11, 15, 25, 0.8);
+  --nav-border: rgba(31, 41, 55, 0.55);
+}
+
+:root.light {
+  /* Light Mode Values */
+  --primary: #2563eb;
+  --primary-glow: rgba(37, 99, 235, 0.08);
+  --secondary: #7c3aed;
+  --bg: #f8fafc;
+  --surface: #ffffff;
+  --surface-border: rgba(0, 0, 0, 0.08);
+  --surface-hover-border: rgba(0, 0, 0, 0.15);
+  --text-primary: #0f172a;
+  --text-secondary: #475569;
+  --nav-bg: rgba(248, 250, 252, 0.8);
+  --nav-border: rgba(0, 0, 0, 0.06);
+}
+
 @theme {
-  --color-primary: #3b82f6;
-  --color-primary-glow: rgba(59, 130, 246, 0.1);
-  --color-secondary: #8b5cf6;
+  --color-primary: var(--primary);
+  --color-primary-glow: var(--primary-glow);
+  --color-secondary: var(--secondary);
   
-  --color-dark-bg: #0b0f19;
-  --color-surface: #111827;
-  --color-surface-border: #1f2937;
-  --color-surface-hover-border: #374151;
-  
-  --color-nav-bg: rgba(11, 15, 25, 0.8);
-  --color-nav-border: rgba(31, 41, 55, 0.55);
+  --color-dark-bg: var(--bg);
+  --color-surface: var(--surface);
+  --color-surface-border: var(--surface-border);
+  --color-surface-hover-border: var(--surface-hover-border);
+  --color-text-primary: var(--text-primary);
+  --color-text-secondary: var(--text-secondary);
 
   --font-outfit: var(--font-outfit), sans-serif;
   --font-inter: var(--font-inter), sans-serif;
@@ -64,37 +93,47 @@
   html {
     scroll-behavior: smooth;
     color-scheme: dark;
+    transition: color-scheme 0.3s ease;
+  }
+  html.light {
+    color-scheme: light;
   }
   
   body {
-    background-color: var(--color-dark-bg);
-    color: #f9fafb;
+    background-color: var(--bg);
+    color: var(--text-primary);
     font-family: var(--font-inter), system-ui, -apple-system, sans-serif;
     min-height: 100vh;
     overflow-x: hidden;
     line-height: 1.6;
+    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease;
   }
   
   h1, h2, h3, h4, h5, h6 {
     font-family: var(--font-outfit), sans-serif;
-    color: #f9fafb;
+    color: var(--text-primary);
     letter-spacing: -0.02em;
+    transition: color 0.3s ease;
+  }
+
+  /* Transition for cards & buttons when theme switches */
+  div, section, header, nav, a, button, input, textarea, span {
+    transition: background-color 0.3s ease, border-color 0.3s ease, color 0.3s ease, box-shadow 0.3s ease;
   }
 }
 
 /* Minimal design utility cards (Stripe/Linear style) */
 @utility glass-panel {
-  background-color: #111827;
-  border: 1px solid #1f2937;
+  background-color: var(--surface);
+  border: 1px solid var(--surface-border);
   border-radius: 18px;
-  transition: all 0.3s cubic-bezier(0.16, 1, 0.3, 1);
 }
 
 @utility glass-panel-hover {
   &:hover {
-    border-color: #374151;
+    border-color: var(--surface-hover-border);
     transform: translateY(-2px);
-    box-shadow: 0 12px 30px -10px rgba(0, 0, 0, 0.5);
+    box-shadow: 0 12px 30px -10px rgba(0, 0, 0, 0.2);
   }
 }
 
@@ -103,25 +142,25 @@
   width: 6px;
 }
 ::-webkit-scrollbar-track {
-  background: var(--color-dark-bg);
+  background: var(--bg);
 }
 ::-webkit-scrollbar-thumb {
-  background: #1f2937;
+  background: var(--surface-border);
   border-radius: 10px;
 }
 ::-webkit-scrollbar-thumb:hover {
-  background: #3b82f6;
+  background: var(--primary);
 }
 
 /* Gradient highlights */
 .gradient-text {
-  background: linear-gradient(135deg, #ffffff 40%, #94a3b8 100%);
+  background: linear-gradient(135deg, var(--text-primary) 40%, var(--text-secondary) 100%);
   -webkit-background-clip: text;
   -webkit-text-fill-color: transparent;
 }
 
 .gradient-accent-text {
-  background: linear-gradient(135deg, #3b82f6 0%, #8b5cf6 100%);
+  background: linear-gradient(135deg, var(--primary) 0%, var(--secondary) 100%);
   -webkit-background-clip: text;
   -webkit-text-fill-color: transparent;
 }

src/components/Hero/Hero.tsx

@@ -34,11 +34,11 @@ export default function Hero() {
           <span className="inline-block w-1.5 h-1.5 bg-primary rounded-full shadow-[0_0_6px_var(--color-primary)]"></span>
           Aspiring Intern
         </div>
-        <h1 className="text-5xl sm:text-7xl font-extrabold mb-6 leading-[1.05] tracking-tighter text-white">
-          Hi, I am <span className="bg-gradient-to-r from-white to-slate-300 bg-clip-text text-transparent">Bui Minh Quan</span>
+        <h1 className="text-5xl sm:text-7xl font-extrabold mb-6 leading-[1.05] tracking-tighter text-text-primary">
+          Hi, I am <span className="bg-gradient-to-r from-text-primary to-text-secondary bg-clip-text text-transparent">Bui Minh Quan</span>
           <span className="bg-gradient-to-r from-primary to-secondary bg-clip-text text-transparent block">Full-Stack Developer</span>
         </h1>
-        <p className="text-base sm:text-lg text-slate-400 mb-8 leading-relaxed max-w-[500px]">
+        <p className="text-base sm:text-lg text-text-secondary mb-8 leading-relaxed max-w-[500px]">
           Information Technology student at PTIT HCMC specializing in Software Engineering. 
           Experienced in building RESTful APIs and modern web applications with Spring Boot, React, and Next.js.
         </p>
@@ -66,7 +66,7 @@ export default function Hero() {
           <a
             href="#contact"
             onClick={(e) => handleScrollTo(e, "contact")}
-            className="bg-[#111827] hover:bg-[#1f2937] text-white border border-white/5 px-7 py-3 rounded-full font-semibold text-[15px] hover:-translate-y-0.5 transition-all duration-200 cursor-pointer"
+            className="bg-surface hover:bg-slate-500/10 text-text-primary border border-surface-border px-7 py-3 rounded-full font-semibold text-[15px] hover:-translate-y-0.5 transition-all duration-200 cursor-pointer"
           >
             Contact Info
           </a>
@@ -107,7 +107,7 @@ export default function Hero() {
           </div>
 
           {/* Floating Skill Badge */}
-          <div className="absolute bg-[#111827] border border-[#1f2937] px-4 py-2 rounded-full text-xs font-semibold text-slate-300 flex items-center gap-2 bottom-8 right-0 sm:right-4 animate-float" style={{ animationDelay: "1s" }}>
+          <div className="absolute bg-surface border border-surface-border px-4 py-2 rounded-full text-xs font-semibold text-text-primary flex items-center gap-2 bottom-8 right-0 sm:right-4 animate-float" style={{ animationDelay: "1s" }}>
             <svg
               width="16"
               height="16"

src/components/Navbar/Navbar.tsx

@@ -14,6 +14,7 @@ export default function Navbar() {
   const [scrolled, setScrolled] = useState(false);
   const [mobileMenuOpen, setMobileMenuOpen] = useState(false);
   const [activeSection, setActiveSection] = useState("home");
+  const [theme, setTheme] = useState<"dark" | "light">("dark");
 
   useEffect(() => {
     const handleScroll = () => {
@@ -28,6 +29,22 @@ export default function Navbar() {
     return () => window.removeEventListener("scroll", handleScroll);
   }, []);
 
+  useEffect(() => {
+    // Check saved theme or preference
+    const savedTheme = localStorage.getItem("theme") as "dark" | "light" | null;
+    if (savedTheme) {
+      setTheme(savedTheme);
+      if (savedTheme === "light") {
+        document.documentElement.classList.add("light");
+      } else {
+        document.documentElement.classList.remove("light");
+      }
+    } else {
+      setTheme("dark");
+      document.documentElement.classList.remove("light");
+    }
+  }, []);
+
   useEffect(() => {
     const sections = NAV_ITEMS.map((item) => document.getElementById(item.id));
     
@@ -56,6 +73,17 @@ export default function Navbar() {
     };
   }, []);
 
+  const toggleTheme = () => {
+    const nextTheme = theme === "dark" ? "light" : "dark";
+    setTheme(nextTheme);
+    localStorage.setItem("theme", nextTheme);
+    if (nextTheme === "light") {
+      document.documentElement.classList.add("light");
+    } else {
+      document.documentElement.classList.remove("light");
+    }
+  };
+
   const handleLinkClick = (e: React.MouseEvent<HTMLAnchorElement>, id: string) => {
     e.preventDefault();
     setMobileMenuOpen(false);
@@ -75,13 +103,13 @@ export default function Navbar() {
   return (
     <header className={`fixed top-0 left-0 w-full z-50 transition-all duration-300 border-b ${
       scrolled 
-        ? "py-3 bg-dark-bg/75 backdrop-blur-md border-white/5 shadow-md" 
+        ? "py-3 bg-dark-bg/75 backdrop-blur-md border-surface-border shadow-md" 
         : "py-6 bg-transparent border-transparent"
     }`}>
       <div className="max-w-[1200px] mx-auto px-6 flex justify-between items-center">
         {/* Logo */}
-        <a href="#home" onClick={(e) => handleLinkClick(e, "home")} className="font-outfit font-bold text-lg text-white flex items-center gap-1.5 tracking-tight">
-          MinhQuan<span className="inline-block w-1.5 h-1.5 bg-primary rounded-full shadow-[0_0_6px_rgba(59,130,246,0.6)]"></span>
+        <a href="#home" onClick={(e) => handleLinkClick(e, "home")} className="font-outfit font-bold text-lg text-text-primary flex items-center gap-1.5 tracking-tight">
+          MinhQuan<span className="inline-block w-1.5 h-1.5 bg-primary rounded-full shadow-[0_0_6px_var(--color-primary)]"></span>
         </a>
 
         {/* Desktop Navigation */}
@@ -94,8 +122,8 @@ export default function Navbar() {
                   onClick={(e) => handleLinkClick(e, item.id)}
                   className={`font-inter text-xs uppercase tracking-wider font-semibold relative py-1 transition-colors duration-200 after:content-[''] after:absolute after:bottom-0 after:left-0 after:w-0 after:h-[1px] after:bg-primary after:transition-all after:duration-250 hover:after:w-full ${
                     activeSection === item.id 
-                      ? "text-white after:w-full" 
-                      : "text-slate-400 hover:text-white"
+                      ? "text-text-primary after:w-full" 
+                      : "text-text-secondary hover:text-text-primary"
                   }`}
                 >
                   {item.label}
@@ -105,35 +133,87 @@ export default function Navbar() {
           </ul>
         </nav>
 
-        {/* CTA Button */}
-        <div className="hidden md:block">
+        {/* Action Controls & CTA */}
+        <div className="hidden md:flex items-center gap-4">
+          {/* Light/Dark Toggle */}
+          <button
+            onClick={toggleTheme}
+            className="w-8 h-8 rounded-full border border-surface-border flex items-center justify-center text-text-secondary hover:text-text-primary hover:border-primary/30 transition-all cursor-pointer"
+            aria-label="Toggle Theme"
+          >
+            {theme === "dark" ? (
+              <svg width="15" height="15" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5">
+                <circle cx="12" cy="12" r="5"></circle>
+                <line x1="12" y1="1" x2="12" y2="3"></line>
+                <line x1="12" y1="21" x2="12" y2="23"></line>
+                <line x1="4.22" y1="4.22" x2="5.64" y2="5.64"></line>
+                <line x1="18.36" y1="18.36" x2="19.78" y2="19.78"></line>
+                <line x1="1" y1="12" x2="3" y2="12"></line>
+                <line x1="21" y1="12" x2="23" y2="12"></line>
+                <line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line>
+                <line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line>
+              </svg>
+            ) : (
+              <svg width="15" height="15" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5">
+                <path d="M21 12.79A9 9 0 1 1 11.21 3 7 7 0 0 0 21 12.79z"></path>
+              </svg>
+            )}
+          </button>
+
           <a
             href="#contact"
             onClick={(e) => handleLinkClick(e, "contact")}
-            className="border border-white/10 text-white px-5 py-2 rounded-full font-medium text-xs tracking-wide hover:border-primary hover:bg-primary/5 transition-all duration-200"
+            className="border border-surface-border text-text-primary px-5 py-2 rounded-full font-semibold text-xs tracking-wide hover:border-primary hover:bg-primary/5 transition-all duration-200"
           >
             Hire Me
           </a>
         </div>
 
-        {/* Mobile Hamburger Toggle */}
-        <button
-          className="md:hidden text-slate-400 hover:text-white focus:outline-none z-50 p-1"
-          onClick={() => setMobileMenuOpen(!mobileMenuOpen)}
-          aria-label="Toggle menu"
-        >
-          <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24" strokeWidth="2.5">
-            {mobileMenuOpen ? (
-              <path strokeLinecap="round" strokeLinejoin="round" d="M6 18L18 6M6 6l12 12" />
+        {/* Mobile Action buttons & Menu Trigger */}
+        <div className="flex md:hidden items-center gap-3">
+          {/* Mobile Theme Toggle */}
+          <button
+            onClick={toggleTheme}
+            className="w-8 h-8 rounded-full border border-surface-border flex items-center justify-center text-text-secondary hover:text-text-primary transition-all cursor-pointer"
+            aria-label="Toggle Theme"
+          >
+            {theme === "dark" ? (
+              <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5">
+                <circle cx="12" cy="12" r="5"></circle>
+                <line x1="12" y1="1" x2="12" y2="3"></line>
+                <line x1="12" y1="21" x2="12" y2="23"></line>
+                <line x1="4.22" y1="4.22" x2="5.64" y2="5.64"></line>
+                <line x1="18.36" y1="18.36" x2="19.78" y2="19.78"></line>
+                <line x1="1" y1="12" x2="3" y2="12"></line>
+                <line x1="21" y1="12" x2="23" y2="12"></line>
+                <line x1="4.22" y1="19.78" x2="5.64" y2="18.36"></line>
+                <line x1="18.36" y1="5.64" x2="19.78" y2="4.22"></line>
+              </svg>
             ) : (
-              <path strokeLinecap="round" strokeLinejoin="round" d="M4 6h16M4 12h16M4 18h16" />
+              <svg width="14" height="14" viewBox="0 0 24 24" fill="none" stroke="currentColor" strokeWidth="2.5">
+                <path d="M21 12.79A9 9 0 1 1 11.21 3 7 7 0 0 0 21 12.79z"></path>
+              </svg>
             )}
-          </svg>
-        </button>
+          </button>
+
+          <button
+            className="text-text-secondary hover:text-text-primary focus:outline-none p-1"
+            onClick={() => setMobileMenuOpen(!mobileMenuOpen)}
+            aria-label="Toggle menu"
+          >
+            <svg className="w-5 h-5" fill="none" stroke="currentColor" viewBox="0 0 24 24" strokeWidth="2.5">
+              {mobileMenuOpen ? (
+                <path strokeLinecap="round" strokeLinejoin="round" d="M6 18L18 6M6 6l12 12" />
+              ) : (
+                <path strokeLinecap="round" strokeLinejoin="round" d="M4 6h16M4 12h16M4 18h16" />
+              )}
+            </svg>
+          </button>
+        </div>
 
         {/* Mobile Menu Dropdown */}
         <div
-          className={`fixed top-0 right-0 w-[75%] max-w-[320px] h-screen bg-[#0e1322] border-l border-white/5 p-8 pt-24 flex flex-col gap-6 z-40 transition-transform duration-300 ease-in-out ${
+          className={`fixed top-0 right-0 w-[75%] max-w-[320px] h-screen bg-surface border-l border-surface-border p-8 pt-24 flex flex-col gap-6 z-40 transition-transform duration-300 ease-in-out ${
             mobileMenuOpen ? "translate-x-0" : "translate-x-full"
           }`}
         >
@@ -146,7 +226,7 @@ export default function Navbar() {
                   className={`font-inter text-sm uppercase tracking-wider font-semibold block py-2 transition-colors ${
                     activeSection === item.id 
                       ? "text-primary" 
-                      : "text-slate-400 hover:text-white"
+                      : "text-text-secondary hover:text-text-primary"
                   }`}
                 >
                   {item.label}
@@ -157,7 +237,7 @@ export default function Navbar() {
           <a
             href="#contact"
             onClick={(e) => handleLinkClick(e, "contact")}
-            className="border border-white/10 text-white py-2.5 rounded-full font-medium text-xs text-center hover:border-primary hover:bg-primary/5 transition-all mt-4"
+            className="border border-surface-border text-text-primary py-2.5 rounded-full font-semibold text-xs text-center hover:border-primary hover:bg-primary/5 transition-all mt-4"
           >
             Hire Me
           </a>