MDL-81816 core_theme: Fix drag and drop box layout

* The new Boostrap color constrast made apparent an visual issue
appearing when we use drag and drop as the outline of the activity
is cut out of the drag/drop image.

theme/boost/scss/moodle/course.scss

@@ -1338,6 +1338,7 @@ $divider-hover-color: $primary !default;
         // Add a border on hover to the activity card (avoiding hover effect in inner activities).
         &:hover:not(:has(.activity:hover)),
         &.selected {
+            // We use outline here to avoid changing the layout everytime we hover.
             outline: $activity-border-width solid $activity-hover-border-color;
             box-shadow: $box-shadow-sm;
             .activityiconcontainer,
@@ -1346,6 +1347,15 @@ $divider-hover-color: $primary !default;
             }
         }
     }
+    .activity.dragging & {
+        border: $activity-border-width solid $activity-hover-border-color;
+        .editing &:hover {
+            // We cancel the outline when dragging because it is not taken into account
+            // in the element/image representing the drag and drop and it cuts out part of the
+            // border.
+            outline: none;
+        }
+    }
 
     // Activity card grid layout.
     .activity-grid {

theme/boost/style/moodle.css

@@ -29226,6 +29226,12 @@ span.editinstructions .alert-link {
 .editing .activity-item.selected .badge {
   mix-blend-mode: multiply;
 }
+.activity.dragging .activity-item {
+  border: 2px solid #0f6cbf;
+}
+.editing .activity.dragging .activity-item:hover {
+  outline: none;
+}
 .activity-item .activity-grid {
   display: grid;
   align-items: center;

theme/classic/style/moodle.css

@@ -29226,6 +29226,12 @@ span.editinstructions .alert-link {
 .editing .activity-item.selected .badge {
   mix-blend-mode: multiply;
 }
+.activity.dragging .activity-item {
+  border: 2px solid #0f6cbf;
+}
+.editing .activity.dragging .activity-item:hover {
+  outline: none;
+}
 .activity-item .activity-grid {
   display: grid;
   align-items: center;