How to reproduce:
1. Open user's provided project "UI Tookit theme bug.zip"
2. Open "SampleScene" Scene
3. Open the theme1.uss file in the Assets folder (make sure that the cursor parameters are: 16 16)
4. Open the test.uxml file in the Assets folder
5. Click on .test under theme1.uss in the top left corner
6. Change Width and Height parameters in the UI Builder's Inspector window and save

Expected result: Only the Width and Height values are changed in the .uss file
Actual result: Width and Height values are changed, but also a comma appears separating the cursor's values

Reproducible with: 1.0.0-preview.18 (2020.3.25f1), 1.0.0 (2021.2.7f1, 2022.1.0b2)
Could not test with: 2019.4.34f1 - UI Builder package is unavailable

Notes:
- USS Preview window in the UI Builder always shows the cursor's values separated with a comma
- "Expected end of value but found '16'" error is thrown after changing parameters in the UI Builder window