Adding dark mode support

layouts/partials/menu_button.html

@@ -3,4 +3,8 @@
         <div class="icon">{{ readFile "static/show-sidebar.svg" | safeHTML }}</div>
         Table of Contents
     </button>
+    <form style="float: right; padding-left: 1rem;">
+        <label for="dark_mode">Dark Mode?</label>
+        <input type="checkbox" id="dark_mode" name="dark_mode" />
+    </form>
 </div>