Converting the epub to mobi and back again seems to work ok on my Kindle which is great.
However the same can't be said for the converted book in the Kindle IOS app.
See the two screenshots below - epub on the left and purchased from store book on the right. The formatting seems massively different.
If I go to Remove Unused CSS in Calibre it says "No used CSS style rules found, No unused CSS selectors found and No unused stylesheets found".
I will post the CSS outputs.