Scrolling in variables pane is broken in light theme

[Yogu]

This issue pertains to the following package(s):

• GraphQL Playground HTML

What OS and OS version are you experiencing the issue(s) on?

Windows 10, Google Chrome 66.0.3359.139

What version of graphql-playground(-electron/-middleware) are you experiencing the issue(s) on?

1.5.5 (with graphql-yoga 1.14.1)

What is the expected behavior?

I can scroll the variables pane and the query independently in light mode as I can in dark mode.

What is the actual behavior?

The variables pane can not be resized normally; if I click into it, it expands a little but it seems as if the whole page just grows over 100%, so the query pane scrolls away. Maybe

What steps may we take to reproduce the behavior?

1. Switch to light mode
2. Open variables pane
3. Enter something and try to scroll in it, or try to resize it