transparent header-bars only for csd windows

gtk-3.0/_common.scss

@@ -1025,11 +1025,15 @@ GtkComboBox {
   border-color: darken($header_bg, 7%);
 
   color: $header_fg;
-  background-color: $header_bg;
+  background-color: opacify($header_bg, 1);
+
+  .csd & { background-color: $header_bg; }  // Transparent header-bars only in csd windows
 
   &:backdrop {
     color: transparentize($header_fg, 0.3);
-    background-color: lighten($header_bg, 3%);
+    background-color: lighten(opacify($header_bg, 1), 3%);
+
+    .csd & { background-color: lighten($header_bg, 3%); }  // Transparent header-bars only in csd windows
   }
 
   .title {

gtk-3.0/gtk-contained.css

@@ -779,10 +779,14 @@ GtkComboBox {
   border-radius: 0;
   border-color: rgba(212, 213, 219, 0.95);
   color: rgba(82, 93, 118, 0.8);
-  background-color: rgba(231, 232, 235, 0.95); }
+  background-color: #e7e8eb; }
+  .csd .header-bar {
+    background-color: rgba(231, 232, 235, 0.95); }
   .header-bar:backdrop {
     color: rgba(82, 93, 118, 0.5);
-    background-color: rgba(239, 240, 242, 0.95); }
+    background-color: #eff0f2; }
+    .csd .header-bar:backdrop {
+      background-color: rgba(239, 240, 242, 0.95); }
   .header-bar .title {
     padding: 0px 12px; }
   .header-bar .subtitle {