Adds color mode toggle and CSS theming.

static/color_mode.js

@@ -0,0 +1,26 @@
+
+document.addEventListener('DOMContentLoaded', () => {
+  const themeToggle = document.getElementById('bd-theme');
+
+  // Check if a theme preference is saved in localStorage
+  const savedTheme = localStorage.getItem('theme');
+  
+  if (savedTheme === 'dark') {
+      themeToggle.checked = true;
+      document.documentElement.setAttribute('data-bs-theme', 'dark');
+  } else {
+      themeToggle.checked = false;
+      document.documentElement.setAttribute('data-bs-theme', 'light');
+  }
+
+  // Add event listener to toggle theme on checkbox change
+  themeToggle.addEventListener('change', () => {
+      if (themeToggle.checked) {
+          document.documentElement.setAttribute('data-bs-theme', 'dark');
+          localStorage.setItem('theme', 'dark');
+      } else {
+          document.documentElement.setAttribute('data-bs-theme', 'light');
+          localStorage.setItem('theme', 'light');
+      }
+  });
+});