diff --git a/app/globals.css b/app/globals.css
index cf67854..3cdf57a 100644
--- a/app/globals.css
+++ b/app/globals.css
@@ -4,14 +4,53 @@
 
 :root {
   color-scheme: light;
+  --background: 210 40% 98%;
+  --foreground: 222 47% 11%;
+  --card: 0 0% 100%;
+  --card-foreground: 222 47% 11%;
+  --muted: 210 20% 96%;
+  --muted-foreground: 215 16% 47%;
+  --border: 214 32% 91%;
+  --input: 214 32% 91%;
+  --ring: 217 91% 60%;
+  --primary: 217 91% 60%;
+  --primary-foreground: 210 40% 98%;
+  --secondary: 191 91% 42%;
+  --secondary-foreground: 210 40% 98%;
+  --accent: 199 89% 48%;
+  --accent-foreground: 210 40% 98%;
+  --destructive: 0 84% 60%;
+  --destructive-foreground: 210 40% 98%;
+}
+
+.dark {
+  color-scheme: dark;
+  --background: 222 47% 8%;
+  --foreground: 210 40% 96%;
+  --card: 222 47% 11%;
+  --card-foreground: 210 40% 96%;
+  --muted: 217 33% 17%;
+  --muted-foreground: 215 20% 65%;
+  --border: 217 33% 20%;
+  --input: 217 33% 20%;
+  --ring: 217 91% 60%;
+  --primary: 217 91% 60%;
+  --primary-foreground: 210 40% 98%;
+  --secondary: 191 91% 42%;
+  --secondary-foreground: 210 40% 98%;
+  --accent: 199 89% 48%;
+  --accent-foreground: 210 40% 98%;
+  --destructive: 0 62% 40%;
+  --destructive-foreground: 210 40% 98%;
 }
 
 * {
   @apply box-border;
+  border-color: hsl(var(--border));
 }
 
 body {
-  @apply bg-slate-50 text-slate-900 antialiased;
+  @apply bg-background text-foreground antialiased;
   font-family: "Inter", system-ui, -apple-system, "Segoe UI", sans-serif;
   background-image:
     radial-gradient(circle at 20% 20%, rgba(59, 130, 246, 0.08), transparent 35%),
@@ -21,7 +60,7 @@ body {
 }
 
 .dark body {
-  @apply bg-slate-950 text-slate-100;
+  @apply bg-background text-foreground;
   background-image:
     radial-gradient(circle at 20% 20%, rgba(59, 130, 246, 0.08), transparent 35%),
     radial-gradient(circle at 80% 0%, rgba(124, 58, 237, 0.12), transparent 30%),
@@ -29,14 +68,31 @@ body {
 }
 
 .card {
-  @apply bg-white/90 shadow-card rounded-2xl border border-slate-100 backdrop-blur;
+  @apply bg-card/90 text-card-foreground shadow-card rounded-2xl border border-border backdrop-blur;
   transition: transform 180ms ease, box-shadow 180ms ease;
-    box-shadow: 0 18px 48px rgba(15, 23, 42, 0.12);
-
+  box-shadow: 0 18px 48px rgba(15, 23, 42, 0.12);
 }
 
 
 .dark .card {
-  @apply bg-slate-900/80 border-slate-800;
+  @apply bg-card/80 border-border;
   box-shadow: 0 18px 48px rgba(0, 0, 0, 0.45);
-}
\ No newline at end of file
+}
+
+html.theme-transition,
+html.theme-transition *,
+html.theme-transition *::before,
+html.theme-transition *::after {
+  transition-property: background-color, border-color, color, fill, stroke, box-shadow;
+  transition-duration: 460ms;
+  transition-timing-function: cubic-bezier(0.32, 0, 0.2, 1);
+}
+
+@media (prefers-reduced-motion: reduce) {
+  html.theme-transition,
+  html.theme-transition *,
+  html.theme-transition *::before,
+  html.theme-transition *::after {
+    transition: none !important;
+  }
+}
diff --git a/app/layout.tsx b/app/layout.tsx
index 1684f24..c6898f4 100644
--- a/app/layout.tsx
+++ b/app/layout.tsx
@@ -9,7 +9,7 @@ export const metadata = {
 
 export default function RootLayout({ children }: { children: ReactNode }) {
   return (
-    <html>
+    <html lang="en" suppressHydrationWarning>
       <body>
         <Providers>{children}</Providers>
       </body>
diff --git a/app/page.tsx b/app/page.tsx
index ed399a9..776ff42 100644
--- a/app/page.tsx
+++ b/app/page.tsx
@@ -6,6 +6,7 @@ import { ResultDashboard } from "../components/result-dashboard";
 import { DashboardSkeleton } from "../components/skeletons";
 import { UserResult } from "@/types/user-result";
 import { LanguageSwitcher } from "@/components/language-switcher";
+import { ThemeToggle } from "@/components/theme-toggle";
 
 type ApiResponse = {
   success: boolean;
@@ -68,7 +69,7 @@ export default function HomePage() {
   return (
     <main className="min-h-screen flex flex-col">
       {" "}
-      <header className="sticky top-0 z-50 w-full border-b bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60">
+      <header className="sticky top-0 z-50 w-full border-b border-border bg-background/95 backdrop-blur supports-[backdrop-filter]:bg-background/60">
         <div className="container flex h-16 max-w-7xl items-center justify-between m-auto px-4">
           <div className="flex items-center gap-2 font-bold text-xl">
             <span className="bg-gradient-to-r from-primary to-primary/60 bg-clip-text text-transparent">
@@ -78,6 +79,7 @@ export default function HomePage() {
 
           <div className="flex gap-4">
             <LanguageSwitcher />
+            <ThemeToggle />
           </div>
         </div>
       </header>
@@ -122,7 +124,7 @@ export default function HomePage() {
           </div>
         )}
       </div>
-      <footer className="border-t py-6 text-center text-sm text-muted-foreground">
+      <footer className="border-t border-border py-6 text-center text-sm text-muted-foreground">
         <div className="container max-w-7xl mx-auto px-4">
           <span className="font-medium">DevImpact</span> — Compare GitHub developer metrics
         </div>
diff --git a/app/providers.tsx b/app/providers.tsx
index 48e0a87..7e97fb0 100644
--- a/app/providers.tsx
+++ b/app/providers.tsx
@@ -2,11 +2,14 @@
 
 import { LanguageProvider } from "@/components/language-provider";
 import { TooltipProvider } from "@/components/ui/tooltip";
+import { ThemeProvider } from "@/components/theme-provider";
 
 export default function Providers({ children }: { children: React.ReactNode }) {
   return (
-    <LanguageProvider>
-      <TooltipProvider>{children}</TooltipProvider>{" "}
-    </LanguageProvider>
+    <ThemeProvider>
+      <LanguageProvider>
+        <TooltipProvider>{children}</TooltipProvider>
+      </LanguageProvider>
+    </ThemeProvider>
   );
 }
diff --git a/components/compare-form.tsx b/components/compare-form.tsx
index e3f4fd7..91e2db9 100644
--- a/components/compare-form.tsx
+++ b/components/compare-form.tsx
@@ -68,14 +68,14 @@ export function CompareForm({
         <CardContent>
           <div className="grid gap-3 md:grid-cols-2">
             <input
-              className="h-11 rounded-lg border border-slate-200 px-3 text-sm focus:outline-none focus:ring-2 focus:ring-primary/60 focus:border-transparent bg-white"
+              className="h-11 rounded-lg border border-input bg-background px-3 text-sm text-foreground placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-primary/60 focus:border-transparent"
               ref={firstInputRef}
               placeholder={t("form.username1") }
               value={username1}
               onChange={(e) => setUsername1(e.target.value)}
             />
             <input
-              className="h-11 rounded-lg border border-slate-200 px-3 text-sm focus:outline-none focus:ring-2 focus:ring-primary/60 focus:border-transparent bg-white"
+              className="h-11 rounded-lg border border-input bg-background px-3 text-sm text-foreground placeholder:text-muted-foreground focus:outline-none focus:ring-2 focus:ring-primary/60 focus:border-transparent"
               placeholder={t("form.username2") }
               value={username2}
               onChange={(e) => setUsername2(e.target.value)}
diff --git a/components/comparison-table.tsx b/components/comparison-table.tsx
index 2fa44d3..0321aad 100644
--- a/components/comparison-table.tsx
+++ b/components/comparison-table.tsx
@@ -32,7 +32,7 @@ const {t} = useTranslation();
             </CardTitle>
           </CardHeader>
           <CardContent className="pt-6 space-y-4">
-            <div className="flex justify-between items-center border-b pb-2">
+            <div className="flex justify-between items-center border-b border-border pb-2">
               <span className="text-muted-foreground">{t("comparsion.final.score")}</span>
               <span className="text-2xl font-bold">{user.finalScore}</span>
             </div>
diff --git a/components/language-switcher.tsx b/components/language-switcher.tsx
index 3d03f04..d4e7d37 100644
--- a/components/language-switcher.tsx
+++ b/components/language-switcher.tsx
@@ -8,7 +8,7 @@ export function LanguageSwitcher() {
   return (
     <div className={cn("flex items-center gap-2 text-sm", dir === "rtl" && "flex-row-reverse")}>
       <select
-        className="h-9 rounded-lg border border-slate-200 bg-white px-3 text-sm focus:outline-none focus:ring-2 focus:ring-primary/60"
+        className="h-9 rounded-lg border border-input bg-background px-3 text-sm text-foreground focus:outline-none focus:ring-2 focus:ring-primary/60"
         value={locale}
         onChange={(e) => setLocale(e.target.value as any)}
       >
diff --git a/components/score-card.tsx b/components/score-card.tsx
index d1ffd2c..db74739 100644
--- a/components/score-card.tsx
+++ b/components/score-card.tsx
@@ -11,17 +11,17 @@ export function ScoreCard({ title, value, highlight, subtitle }: ScoreCardProps)
   return (
     <div
       className={cn(
-        "card p-4 flex flex-col gap-1 border bg-gradient-to-br from-white via-white to-slate-50 transition-all",
-        highlight ? "border-blue-500/50 shadow-blue-200" : "border-slate-100"
+        "card p-4 flex flex-col gap-1 border bg-gradient-to-br from-card via-card to-muted/40 transition-all",
+        highlight ? "border-primary/50 shadow-blue-200 dark:shadow-blue-950/40" : "border-border"
       )}
     >
-      <p className="text-xs uppercase tracking-wide text-slate-500">{title}</p>
+      <p className="text-xs uppercase tracking-wide text-muted-foreground">{title}</p>
       <div className="flex items-baseline gap-2">
-        <span className="text-2xl font-semibold text-slate-900">
+        <span className="text-2xl font-semibold text-foreground">
           {value.toFixed(2)}
         </span>
         {subtitle && (
-          <span className="text-xs text-slate-500 leading-tight">{subtitle}</span>
+          <span className="text-xs text-muted-foreground leading-tight">{subtitle}</span>
         )}
       </div>
     </div>
diff --git a/components/skeletons.tsx b/components/skeletons.tsx
index 21613ce..f3e3c46 100644
--- a/components/skeletons.tsx
+++ b/components/skeletons.tsx
@@ -1,13 +1,15 @@
+import { Skeleton } from "@/components/ui/skeleton";
+
 export function DashboardSkeleton() {
   return (
     <div className="card p-6 animate-pulse space-y-4">
-      <div className="h-5 bg-slate-200 rounded w-1/3" />
-      <div className="h-4 bg-slate-200 rounded w-1/2" />
+      <Skeleton className="h-5 w-1/3" />
+      <Skeleton className="h-4 w-1/2" />
       <div className="grid gap-3 md:grid-cols-2">
-        <div className="h-24 bg-slate-200 rounded-lg" />
-        <div className="h-24 bg-slate-200 rounded-lg" />
+        <Skeleton className="h-24 rounded-lg" />
+        <Skeleton className="h-24 rounded-lg" />
       </div>
-      <div className="h-64 bg-slate-200 rounded-xl" />
+      <Skeleton className="h-64 rounded-xl" />
     </div>
   );
 }
diff --git a/components/theme-provider.tsx b/components/theme-provider.tsx
new file mode 100644
index 0000000..75a06f3
--- /dev/null
+++ b/components/theme-provider.tsx
@@ -0,0 +1,17 @@
+"use client";
+
+import { ThemeProvider as NextThemesProvider } from "next-themes";
+import type { ReactNode } from "react";
+
+export function ThemeProvider({ children }: { children: ReactNode }) {
+  return (
+    <NextThemesProvider
+      attribute="class"
+      defaultTheme="system"
+      enableSystem
+      storageKey="devimpact-theme"
+    >
+      {children}
+    </NextThemesProvider>
+  );
+}
diff --git a/components/theme-toggle.tsx b/components/theme-toggle.tsx
new file mode 100644
index 0000000..ccae4ee
--- /dev/null
+++ b/components/theme-toggle.tsx
@@ -0,0 +1,43 @@
+"use client";
+
+import { Moon, Sun } from "lucide-react";
+import { useTheme } from "next-themes";
+import { Button } from "./ui/button";
+import { useEffect, useState } from "react";
+
+export function ThemeToggle() {
+  const { theme, setTheme, resolvedTheme } = useTheme();
+  const [mounted, setMounted] = useState(false);
+  useEffect(() => setMounted(true), []);
+  const THEME_TRANSITION_MS = 520;
+
+  const current = resolvedTheme || theme || "light";
+  const next = current === "light" ? "dark" : "light";
+
+  const handleToggle = () => {
+    if (typeof document !== "undefined") {
+      const root = document.documentElement;
+      root.classList.add("theme-transition");
+      window.setTimeout(() => {
+        root.classList.remove("theme-transition");
+      }, THEME_TRANSITION_MS);
+    }
+
+    requestAnimationFrame(() => {
+      setTheme(next);
+    });
+  };
+
+  return (
+    <Button
+      type="button"
+      variant="ghost"
+      size="sm"
+      onClick={handleToggle}
+      className="flex items-center gap-2"
+      aria-label="Toggle color mode"
+    >
+      {mounted && current === "dark" ? <Sun size={16} /> : <Moon size={16} />}
+    </Button>
+  );
+}
diff --git a/components/top-list.tsx b/components/top-list.tsx
index b545b75..bafd405 100644
--- a/components/top-list.tsx
+++ b/components/top-list.tsx
@@ -30,11 +30,11 @@ export function TopList({ userResults }: Props) {
     key: string | number;
   }) => (
     <div
-      className="rounded-lg border p-3 transition-all hover:bg-muted/50 flex items-center justify-between"
+      className="rounded-lg border border-border p-3 transition-all hover:bg-muted/50 flex items-center justify-between"
       key={data.key}
     >
       <div>
-        <div className="font-medium text-slate-900">
+        <div className="font-medium text-foreground">
           {data.titleUrl ? (
             <a
               href={data.titleUrl}
@@ -67,10 +67,10 @@ export function TopList({ userResults }: Props) {
         </div>
       </div>
       <div className="text-right">
-        <p className="text-sm font-semibold text-slate-900">
+        <p className="text-sm font-semibold text-foreground">
           {(data.score ?? 0).toFixed(2)}
         </p>
-        <p className="text-[11px] text-slate-500">{t('comparsion.score')}</p>
+        <p className="text-[11px] text-muted-foreground">{t('comparsion.score')}</p>
       </div>
     </div>
   );
diff --git a/components/ui/input.tsx b/components/ui/input.tsx
new file mode 100644
index 0000000..d763cd9
--- /dev/null
+++ b/components/ui/input.tsx
@@ -0,0 +1,19 @@
+import * as React from "react"
+
+import { cn } from "@/lib/utils"
+
+function Input({ className, type, ...props }: React.ComponentProps<"input">) {
+  return (
+    <input
+      type={type}
+      data-slot="input"
+      className={cn(
+        "h-8 w-full min-w-0 rounded-lg border border-input bg-transparent px-2.5 py-1 text-base transition-colors outline-none file:inline-flex file:h-6 file:border-0 file:bg-transparent file:text-sm file:font-medium file:text-foreground placeholder:text-muted-foreground focus-visible:border-ring focus-visible:ring-3 focus-visible:ring-ring/50 disabled:pointer-events-none disabled:cursor-not-allowed disabled:bg-input/50 disabled:opacity-50 aria-invalid:border-destructive aria-invalid:ring-3 aria-invalid:ring-destructive/20 md:text-sm dark:bg-input/30 dark:disabled:bg-input/80 dark:aria-invalid:border-destructive/50 dark:aria-invalid:ring-destructive/40",
+        className
+      )}
+      {...props}
+    />
+  )
+}
+
+export { Input }
diff --git a/components/ui/skeleton.tsx b/components/ui/skeleton.tsx
new file mode 100644
index 0000000..0118624
--- /dev/null
+++ b/components/ui/skeleton.tsx
@@ -0,0 +1,13 @@
+import { cn } from "@/lib/utils"
+
+function Skeleton({ className, ...props }: React.ComponentProps<"div">) {
+  return (
+    <div
+      data-slot="skeleton"
+      className={cn("animate-pulse rounded-md bg-muted", className)}
+      {...props}
+    />
+  )
+}
+
+export { Skeleton }
diff --git a/next-env.d.ts b/next-env.d.ts
index c4b7818..9edff1c 100644
--- a/next-env.d.ts
+++ b/next-env.d.ts
@@ -1,6 +1,6 @@
 /// <reference types="next" />
 /// <reference types="next/image-types/global" />
-import "./.next/dev/types/routes.d.ts";
+import "./.next/types/routes.d.ts";
 
 // NOTE: This file should not be edited
 // see https://nextjs.org/docs/app/api-reference/config/typescript for more information.
diff --git a/tailwind.config.ts b/tailwind.config.ts
index 64e9b95..811389d 100644
--- a/tailwind.config.ts
+++ b/tailwind.config.ts
@@ -10,34 +10,34 @@ const config: Config = {
   theme: {
     extend: {
       colors: {
-        border: "hsl(210 24% 90%)",
-        input: "hsl(210 24% 90%)",
-        ring: "#3B82F6",
-        background: "hsl(0 0% 100%)",
-        foreground: "hsl(222 47% 11%)",
+        border: "hsl(var(--border))",
+        input: "hsl(var(--input))",
+        ring: "hsl(var(--ring))",
+        background: "hsl(var(--background))",
+        foreground: "hsl(var(--foreground))",
         muted: {
-          DEFAULT: "hsl(210 20% 96%)",
-          foreground: "hsl(215 16% 47%)",
+          DEFAULT: "hsl(var(--muted))",
+          foreground: "hsl(var(--muted-foreground))",
         },
         card: {
-          DEFAULT: "hsl(0 0% 100%)",
-          foreground: "hsl(222 47% 11%)",
+          DEFAULT: "hsl(var(--card))",
+          foreground: "hsl(var(--card-foreground))",
         },
         primary: {
-          DEFAULT: "#3B82F6",
-          foreground: "#F8FBFF",
+          DEFAULT: "hsl(var(--primary))",
+          foreground: "hsl(var(--primary-foreground))",
         },
         secondary: {
-          DEFAULT: "#22D3EE",
-          foreground: "#F8FBFF",
+          DEFAULT: "hsl(var(--secondary))",
+          foreground: "hsl(var(--secondary-foreground))",
         },
         accent: {
-          DEFAULT: "#0EA5E9",
-          foreground: "#F8FBFF",
+          DEFAULT: "hsl(var(--accent))",
+          foreground: "hsl(var(--accent-foreground))",
         },
         destructive: {
-          DEFAULT: "hsl(0 84% 60%)",
-          foreground: "hsl(210 40% 98%)",
+          DEFAULT: "hsl(var(--destructive))",
+          foreground: "hsl(var(--destructive-foreground))",
         },
       },
       boxShadow: {
