💻 Margin login, cheatsheet and language buttons and scrollbar (#5325)

Fixes #4618 , I've also added some margin to the _cheatsheet dropdown button_ and the _language dropdown button_ so that those look nicely aligned. 

**How to test**
On a small screen, see if the buttons have a bit more space between them and the scrollbar so that it looks less crowded.

<img width="345" alt="Screenshot 2024-03-27 at 15 09 44" src="https://github.com/hedyorg/hedy/assets/48122190/3788d75a-9dce-4fb0-9383-8986cada4f1f">

<img width="345" alt="Screenshot 2024-03-27 at 15 10 04" src="https://github.com/hedyorg/hedy/assets/48122190/2c00058a-47cb-49ab-bb13-6fe903bec452">

templates/incl/menubar.html

@@ -67,7 +67,7 @@
               </div>
           </div>
       </li>
-      <a class="blue-btn" href="/login">{{_('login')}}</a>
+      <a class="blue-btn mr-3" href="/login">{{_('login')}}</a>
     {% endif %}
     {% endblock %}
     </ul>

templates/level-page.html

@@ -79,7 +79,7 @@
     {% endif %}
     {% if not hide_cheatsheet and cheatsheet %}
     <div class="dropdown relative">
-      <button class="green-btn font-semibold rounded inline-flex items-center gap-2" id="dropdown_cheatsheet_button"
+      <button class="green-btn font-semibold rounded inline-flex items-center gap-2 mr-2" id="dropdown_cheatsheet_button"
         onclick="$('#cheatsheet_dropdown').slideToggle('medium');">
         <span>{{ "🤔" }}</span>
         <svg id="cheatsheet-arrow" class="fill-current h-6 w-6" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20">
@@ -115,7 +115,7 @@ <h2 class="px-2 py-6">{{_('cheatsheet_title')}}</h2>
     {% endif %}
     {% if get_syntax_language(g.lang) != "en" and (not customizations or 'hide_keyword_switcher' not in customizations['other_settings']) %}
       <div class="dropdown relative">
-        <button class="green-btn font-semibold rounded inline-flex items-center gap-2"
+        <button class="green-btn font-semibold rounded inline-flex items-center gap-2 mr-2"
           onclick="$('#commands_dropdown').slideToggle('medium');" data-cy="kwlang-switch-btn">
           <span class="fa-solid fa-language"></span>
           <svg id="keyword-arrow" class="fill-current h-6 w-6" xmlns="http://www.w3.org/2000/svg" viewBox="0 0 20 20">