Improve handling of oversized ad content

Author: iMattPro

styles/all/theme/phpbbads.css

@@ -1,7 +1,18 @@
 .phpbb-ads {
+	overflow: hidden;
 	margin: 10px 0;
 }
 
+.phpbb-ads img {
+	max-width: 100%;
+	height: auto;
+}
+
+.phpbb-ads iframe,
+.phpbb-ads video {
+	max-width: 100%;
+}
+
 .phpbb-ads-center {
 	text-align: center;
 }