fix(header): collapsable header should default to using content backg…

…round (#20736)

fixes #20691

core/src/components/header/header.ios.scss

@@ -50,7 +50,13 @@
   z-index: 1;
 }
 
+/**
+ * Large title toolbar should just use the content background
+ * since it needs to blend in with the header above it.
+ */
 .header-collapse-condense ion-toolbar {
+  --background: var(--ion-background-color, #fff);
+
   z-index: 0;
 }
 
@@ -81,4 +87,4 @@
 .header-collapse-condense-inactive.header-collapse-condense ion-toolbar.in-toolbar ion-title,
 .header-collapse-condense-inactive.header-collapse-condense ion-toolbar.in-toolbar ion-buttons.buttons-collapse {
   visibility: hidden;
-}
+}