1854108 - Expand default styling for common-use scenerios

Status: NEW

(Toolkit :: UI Widgets, task)

Description

[Sarah Clements [:sclements] | PTO until Oct 12th]

In bug 1845333, submenu support was added however there were a few style changes made that are necessary to support this were added in the firefoxview-next.css file to support this that should be baked into the panel-item.css and panel-list.css style sheets.

These are:

1. y-overflow: auto here is needed for migration wizard and potentially addons, but this prevents the submenu panel from "opening", so it was overriden in firefoxview-next.css

2. padding-inline-start: 32px in panel-item.css is needed for addons and migration wizard for use with icons. But I think there should be support for a simple, common use case where no icons are needed and 12px would suffice. Perhaps an attribute could be used for wide-padding or with-icon so that this doesn't need to be supplied by the consumer, like we have by overriding that style in the panel-item in firefoxview-next.css. And with the way that the submenu panel-list is slotted in, it makes it tricky and a bit messy to try to override default styles.