I have no idea why, but my extended class is completely ignored upon initialization. I think it is a sort of bug, but related strictly to dl element. Demo: https://showcase.builderius.io/examples/examples-for-module-accordion/ I am checking it with Safari 16.0 and 16.1 - it does not work.
Extending of UL works in all browsers: https://showcase.builderius.io/examples/examples-for-module-dynamic-ulist/
Extending TABLE also works in all browsers: https://wpbuildersfightclub.org/
It seems like only extending of DL does not work specifically in Safari.