fix(material/core): ensure that option inherits container background

Fixes that `mat-option` was inheriting its background color from the MDC list which led to issues in M3. The option should always have the same background as its container.

Author: crisbeto

src/material/core/option/option.scss

@@ -53,11 +53,16 @@
     }
   }
 
-  // If the MDC list is loaded after the option, this gets overwritten which breaks the text
-  // alignment. Ideally we'd wrap all the MDC mixins above with this selector, but the increased
-  // specificity breaks some internal overrides.
   &.mdc-list-item {
+    // If the MDC list is loaded after the option, this gets overwritten which breaks the text
+    // alignment. Ideally we'd wrap all the MDC mixins above with this selector, but the increased
+    // specificity breaks some internal overrides.
     align-items: center;
+
+    // List items in MDC have a default background color which can be different from the container
+    // in which the option is projected. Set the base background to transparent since options
+    // should always have the same color as their container.
+    background: transparent;
   }
 
   // Set the `min-height` here ourselves, instead of going through