Resolve "Banner sind zu groß"

Closes #2943

Merge request studip/studip!1983

lib/models/Banner.class.php

@@ -226,6 +226,6 @@ class Banner extends SimpleORMap
         $this->views += 1;
         $this->store();
 
-        return sprintf('<div style="padding: 5px; text-align: center;">%s</div>', $link);
+        return sprintf('<div class="studip-banner">%s</div>', $link);
    }
 }

resources/assets/stylesheets/scss/start.scss

@@ -213,3 +213,12 @@ div.available-widgets {
         }
     }
 }
+
+
+.studip-banner {
+    padding-bottom: 5px;
+    text-align: center;
+    img {
+        max-width: 100%;
+    }
+}