How to reproduce:
1. Create a new Unity project with a LWRP template
2. Create an 'Area Light' GameObject and select it

Expected result: the 'Cast Shadows' option in the Inspector window is not obscured and can be toggled with the mouse
Actual result: the 'Cast Shadows' option in the Inspector window is obscured and cannot be toggled with the mouse

Reproducible with: 2018.3.0a3, 2018.3.0b5, 2019.1.0a4
Not reproducible with: 2018.2.11f1
Could not test with: 2018.3.0a1, 2018.3.0a2

Notes:
Doesn't seem to be the package issue as the same package version was used for testing 2018.2.11f1 and 2018.3.0a3
One can still toggle the option by selecting it with the 'Tab' key and pressing 'Enter'
In older alpha versions of 2018.3, the issue is present in the 'Rectangular Light' GameObject