Kindle for iOS - issue with borders?

I am having a bit of trouble with borders in a book I am formatting.
I added a "border-top" and "border-bottom" to the chapter titles and it shows right in Kindle Previewer on every device except for Kindle for iOS (and old Kindles that don't support borders at all).

But in Kindle for iOS there is border around the text, not just top and bottom, but left and right also.
I tried adding "border-left" & "border-right: none" or "0px", but when I added that all borders disappeared in Kindle for iOS - but still looked right on other devices.
Is there a way to add borders to only 1, 2 or 3 sides of a div in Kindle for iOS? Has anyone had similar experiences before?

I don't have an iOS device to test directly, only Kindle Previewer, my Kindle Paperwhite and Kindle for Android.

Is this border thing in Kindle for iOS a known issue?

Thanks,
-V