Add styling to make "Merge Favorites" appear aligned (in Import Bookmark modal)

[srirambv]

Did you search for similar issues before submitting this one?
Yes

Describe the issue you encountered:
Merge Favourite into bookmark not properly aligned in Import Bookmark modal

Expected behavior:
Should be properly aligned

• Platform (Win7, 8, 10? macOS? Linux distro?):
  Windows 10 x64
• Brave Version:
  0.12.2 RC1
• Steps to reproduce:
  1. Open preferences, Click on Import Bookmarks
  2. Merge Favourite into Bookmark is not properly aligned
     3.
• Screenshot if needed:
  
• Any related issues:
  cc: @darkdh

[darkdh]

This is intended because it is the sub option of importing bookmark.
Maybe we need other way to present the sub option, @bradleyrichter?

[bradleyrichter]

This will be improved soon:

[bsclifton]

Let's reopen and use this to track the change @bradleyrichter has shown 😄

[bradleyrichter]

@cezaraugusto just made a new, smaller switch style so we only need the "L"...

[luixxiul]

Closing this in favor of #7194, 46e3919