Twenty Twelve: submenu hidden under slideshow block

[robertghetau]

This is a replica of this issue: ​https://github.com/Automattic/wp-calypso/issues/63939

Steps to replicate:

1. Activate the theme Twenty Twelve
2. Add 3 elements to the same submenu on the site
3. Add a slideshow at the start of a page

[sabernhardt]

I wanted to say that this should be solved in Jetpack, not the theme. However, the submenus only have a z-index of 1, so any content element with a positive z-index could cover the submenu.

@media screen and (min-width: 600px) {
	.main-navigation li ul {
		z-index: 1;
	}
}