studio - further small cleanup on Sass

cms/static/sass/_base.scss

@@ -455,14 +455,6 @@ code {
 // ====================
 
 // UI - chrome
-.window {
-  @include clearfix();
-  @include border-radius(3px);
-  @include box-shadow(0 1px 1px $shadow-l1);
-  margin-bottom: $baseline;
-  border: 1px solid $gray-l2;
-  background: $white;
-}
 
 // ====================
 

common/static/sass/_mixins.scss

-// all - utilities - mixins and extends
+// studio - utilities - mixins and extends
 // ====================
 
 // font-sizing
@@ -151,4 +151,22 @@
   border: none;
 }
 
-// extends - ui
\ No newline at end of file
+// extends - ui
+.window {
+  @include clearfix();
+  @include border-radius(3px);
+  @include box-shadow(0 1px 1px $shadow-l1);
+  margin-bottom: $baseline;
+  border: 1px solid $gray-l2;
+  background: $white;
+}
+
+.elem-d1 {
+  @include clearfix();
+  @include box-sizing(border-box);
+}
+
+.elem-d2 {
+  @include clearfix();
+  @include box-sizing(border-box);
+}
\ No newline at end of file