fixes #3951

Closes #3951

Merge request studip/studip!2809

resources/assets/stylesheets/scss/talk-bubble.scss

@@ -8,6 +8,13 @@ $ownColor: var(--petrol-40);
 
     .talk-bubble-avatar {
         padding: 8px;
+        width: 40px;
+        height: 40px;
+
+        img {
+            width: 100%;
+            height: 100%;
+        }
     }
 
     .talk-bubble {
@@ -136,4 +143,4 @@ $ownColor: var(--petrol-40);
             flex-direction: row-reverse;
         }
     }
-}
\ No newline at end of file
+}