Hey this a guide detailing how to create hidden text on any Steam bio. The hidden text relies on a bug with spoiler text being used in conjunction with header text (h1 tags + spoiler tags), it basically makes the text hidden. The text can then be shown when the bugged black spoiler bars are highlighted, which can hide an entire bio's worth of text. Not sure if this is a known bug but I didn't find any other guides upon researching.

To my knowledge, the spoiler bars won't overlap onto header text unlike normal text in a bio would, this means that the bars are cut off and don't overlap the text. However they appear as invisible whilst having an effect on the below text.