Added dark mode support with a checkbox

I added a checkbox with for enabling and disabling dark mode and added the functionality. Of course, dark colors, position of the checkbox can all be improved but focused more on the functionality itself and hopefully its gets accepted.

src/app.html

@@ -51,8 +51,29 @@
           <div style="margin-top: 5px">
             <a href="https://mechvibes.com" class="open-in-browser">Check it out</a>
           </div>
+          <!-- PART FOR DARK MODE CHECKBOX-->
+          <input type="checkbox" id="theme-checkbox"> Dark Mode</input>
         </div>
       </div>
     </div>
   </body>
 </html>
+
+<script>
+  //javascript for dark mode checkbox
+  let themeCheck = document.getElementById("theme-checkbox");
+  if(themeCheck.enabled){
+    document.body.style.backgroundColor = "#0A0E12"; //dark mode color i picked but of course can be changed
+    document.body.style.color = "white";
+  }
+  else{
+
+    document.body.style.backgroundColor = "white"; //dark mode color i picked but of course can be changed
+    document.body.style.color = "black";
+
+  }
+
+  #All colors can be changed i just implented the functionality it self.
+
+</script>
+<!--END DARK MODE CHECKBOX-->