Bug, feature request, or proposal:

Bug? Reading the source, when having a menu open, I believe the background should be able to be scrolled using the mouse. The background can be scrolled with the arrow keys.

What is the expected behavior?

The background can scroll.

What is the current behavior?

The background cannot scroll.

What are the steps to reproduce?

1. Visit https://material.angular.io/components/menu/overview
2. Open the menu by clicking the trigger: "Menu"
3. Attempt to scroll the page (not the menu) using the mouse.

What is the use-case or motivation for changing an existing behavior?

A dialog box should block background scrolling, but the menu should not.

Which versions of Angular, Material, OS, TypeScript, browsers are affected?

Current

Is there anything else we should know?

It is blocked by pointer-events: auto: https://github.com/angular/material2/blob/4d82f833c7e4a22814b8e225f05ef4ba01a86ad6/src/cdk/overlay/_overlay.scss#L61.
The menu does have the scroll strategy of reposition, which I believe should mean that the background should be able to be scrolled: https://github.com/angular/material2/blob/fe37cb2551929844d5467e1b9bf45032df35981f/src/lib/menu/menu-trigger.ts#L57