fix: shrink custom element baseline a bit

[dummdidumm]

• use shorter class property names as they are not minified
• reuse some dom helper methods

#8826

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Tests and linting

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[benmccann]

I would put comments next to each of these with their old names or describing what they hold as it might be hard to figure out from just the single-letter abbreviation

[gtm-nayan]

Preferably JSDoc comments above so that they show up when hovering over where the properties are used.