fix: click outside if mounted in shadow DOM

[kelunik]

See https://www.dom-tricks.com/click-outside for details.

Demo for shadow DOM is not styled, not sure how styles are built. Feel free to remove the demo again after testing.

[coveralls]

Pull Request Test Coverage Report for Build 214

• 5 of 12 (41.67%) changed or added relevant lines in 1 file are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage decreased (-0.7%) to 87.118%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/popup.vue	5	12	41.67%

Totals
Change from base Build 212:	-0.7%
Covered Lines:	766
Relevant Lines:	836

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💛 - Coveralls