Header is taller if custom RPC is selected

[wbt]

Describe the bug
The header portion of the MetaMask UI is slightly taller when connecting to a custom RPC, throwing off other vertical alignment around what might be visible with vs. without scrolling.

To Reproduce
Steps to reproduce the behavior:

1. Open a browser with MetaMask and log in.
2. Connect to a custom RPC network.
3. Go to Settings -> About Us (a bit harder to find due to Issue Clicking "Info & Help" doesn't produce expected results #6441)
4. Observe how "Visit our Support Center" appears partially cut off, not part of what the user is intended to be able to see/interact with until after additional scroll action.
   
5. Connect to the Main Ethereum Network
6. Observe how less of the text is cut off:
   

Expected behavior
Custom RPC settings permit a custom icon/color picker, and the default has the same height as the networks that come pre-programmed in.

Browser details (please complete the following information):

• OS: Windows 10 Pro
• Browser: Chrome 72.0.3626.121 (Official Build) (64-bit)
• MetaMask Version: 6.3.1

[wbt]

Is there a PR which fixes this, regarding the closure?

[bdresser]

#6468