"New Brush" button is clipped behind "brush size" value field

Steps to repro:
1. Open attached or create a new project
2. Hierarchy > right click
3. 3D object > terrain
4. Paint terrain tab > Raise or lower terrain
5. Observe the "New Brush" button

Actual Result:
1. the button is clipped behind "brush size" value field

Occurring with:
2018.3.0a9 (1671df2d9715), 2018.3.0a8

Note:
"New Brush" button is added in 2018.3.0a8

Environment:
Windows and Mac