Reports

We'll forget about the right way to do thing and just fix your code.

Firstly, why all that?

tile.classList.add('date_active');
imgSelect.classList.add('tl_LegImgVisible');
imgSelect.setAttribute('aria-hidden', false);
legendSelect.classList.add('tl_LegImgVisible');
legendSelect.removeAttribute('inert');
credSelect.classList.add('credShow');

And not something like that ?

// assume item is a wrapper or each timeline item
item.setAttribute('aria-hidden', false);

And secondary, you issue is related to opacity so where is the CSS code because I don't see where you update it and assume that it is in your CSS code.

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