feat: Tailwind config with dark mode class strategy

frontend/tailwind.config.js

@@ -1,6 +1,21 @@
 /** @type {import('tailwindcss').Config} */
 export default {
   content: ['./index.html', './src/**/*.{js,ts,jsx,tsx}'],
-  theme: { extend: {} },
+  darkMode: 'class',
+  theme: {
+    extend: {
+      colors: {
+        primary: {
+          DEFAULT: '#10b981',
+          dark: '#059669',
+        },
+        'background-light': '#ffffff',
+      },
+      fontFamily: {
+        sans: ['-apple-system', 'BlinkMacSystemFont', 'Inter', 'Segoe UI', 'Roboto', 'sans-serif'],
+        mono: ['JetBrains Mono', 'Fira Code', 'Menlo', 'Monaco', 'monospace'],
+      },
+    },
+  },
   plugins: [],
 }