Edit Trees, refresh, mass place trees button touches the component's margin below, in the inspector window when trees are not assigned or selected

Steps to Repro:
1. Create a new project
2. Hierarchy > right click
3. 3D object > terrain
4. Select paint trees tab
5. Observe Edit Trees, refresh, mass place trees button

Note:
Earlier light map options were available under these buttons, now the lightmap options are only available under terrain settings

Actual Result:
1. Spacing is missing under the buttons, as a result, they touch the component below when trees are not assigned or selected

Expected Result:
1. There should be some marginal spacing below the buttons

Occurring with:
2018.3.0a8, 2018.3.0a6

Working with:
2018.3.0a5

Note:
New Terrain tools are introduced from alpha 2018.3.0a4

Environment:
Windows and Mac