Describe the bug
Doing some of the word in italic covers over the letters beside it.
To Reproduce
Steps to reproduce the behavior:
Expected behavior
Not to cover the letter beside that is not italic
Screenshots

Desktop (please complete the following information):
I tested this as well - when I added the italic text, the initial letter _was_ covered. As soon as I clicked off the word, the italic text and non-italic text were unhighlighted and visible.
Screencast here: http://cld.wthms.co/b8zQku
OS: macOS 10.13.6
Browser: Chrome Version 69.0.3497.100
Gutenberg version 4.1.1
This feels like a bit of an edge case to me which may be acceptable because I noticed in @jesscga's screencast that the problem only shows up when the inline boundary is active with the caret placed inside the italic text. However, it would be good to get a second opinion so I've added the Needs Design Feedback label to see if we can get a check on that.
I feel for now in confines of what we have this could be acceptable. However, let's put to 5.0.1 and see if it can be iterated.
This is "purely" a styling issue. Removing the padding and (negative) margin from selected <em> tags (and any other selected tags that have inline boundaries) seems to fix it.
Before (the last letter before the selection is not visible):

After (all letters are visible):

Thanks for taking care of this issue @iseulde Ella!
I look forward to trying this out in the next GB version as I have seen in a few instances that the last letter gets partly covered up. Example paragraph text, caption etc.