“Enketo-powered web forms only support Markdown styling. Styling is not yet supported in web form choice labels.”
See documentation (ODK) Form Styling - ODK Docs
(and your previous post concerning colour for labels https://community.kobotoolbox.org/t/change-the-color-and-font-appearance-of-the-options-sheet/13167/11.
It works well in Collect.
But it seems to work (almost) for Enketo if you insert the exponent as symbols in Excel in the label text.
But as you see, the positioning is not optimal. (I couldn’t change it, e.g by resizing.)
For Enketo, you might also use a workaround, e.g. 10**18 or 10^18 or (10)power18.
(Be careful in Collect: * has special meaning. You would need to mask it as \*)
