The shape and shading of recipe book tabs are incorrect and inconsistent

The Bug:

The shape and shading of recipe book tabs are incorrect and inconsistent.

Steps to Reproduce:

1. Switch to survival mode and open the recipe book.
2. Look at the shading of the recipe book tabs and notice how the upper and lower parts are 1 pixel wide, instead of 2 pixels wide like the sides.
3. Look at the lower left corner of the recipe book tab and notice how it's different from the lower left corner of the advancement tab.

Observed Behavior:

The shape and shading of recipe book tabs are incorrect and inconsistent.

Expected Behavior:

The shape and shading of recipe book tabs would be correct and consistent.