I'm resurrecting this old thread because I would like that too.
The dogear icon in Koreader is so small, I'd like it a bit bigger.
For comparison, I attach 2 images: 1 is Koreader, 2 the default Kobo interface
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I tried looking at the page linked above, but it seems that the focus shifts to other issues at some point and the thread gets closed because the OP is happy with an alternative solution.
I still don't know how you can enlarge the icon that to me it seems too tiny (if it's even possible to).
Thanks