[FIX] website_slides: fix sidebar overlay

In the course fullscreen view, a black overlay is
hovering the content on medium screen size and lower
when the sidebar is active.

Fix the black overlay which is still showing after
closing the sidebar. When the sidebar is close the
overlay shouldn't be displayed.

As the content is translated to the right and still
fully visible on medium screen size, a black overlay
isn't needed. Only show the black overlay for small
screen size and lower.

Task-3371743

closes odoo/odoo#125036

Signed-off-by: Warnon Aurélien (awa) <awa@odoo.com>

addons/website_slides/static/src/scss/slides_slide_fullscreen.scss

@@ -56,7 +56,7 @@
             }
         }
 
-        @include media-breakpoint-up (md) {
+        @include media-breakpoint-up (sm) {
             width: $o-wslides-fs-side-width;
 
             &.o_wslides_fs_sidebar_hidden {

addons/website_slides/views/website_slides_templates_lesson_fullscreen.xml

@@ -88,7 +88,7 @@
                             </t>
                         </ul>
                     </div>
-                    <a href="#" class="o_wslides_fs_toggle_sidebar d-lg-none bg-black-50"/>
+                    <a href="#" class="o_wslides_fs_toggle_sidebar d-md-none bg-black-50"/>
                 </div>
             </div>
         </div>