Improve custom application templates compatibility

jet/static/jet/css/_base.scss

@@ -53,6 +53,11 @@ a:hover {
   padding: 20px;
 }
 
+.module {
+  border: 0;
+  margin: 0;
+}
+
 @import "table";
 @import "buttongroup";
 @import "sidebar";

jet/static/jet/css/_changeform.scss

@@ -1,12 +1,6 @@
 @import "globals";
 
 .module {
-  border: 0;
-  margin: 0;
-  padding: 20px;
-  background-color: $content-background-color;
-  border-radius: 4px;
-
   .form-row {
     padding: 6px 0;
     overflow: hidden;