Edit form background color on highlighted note

## What does this MR do?

Added white background to edit form when in a highlighted note

## What are the relevant issue numbers?

Closes #18101 

## Screenshots (if relevant)

![Screen_Shot_2016-06-02_at_11.24.20](/uploads/c7c7fe710aa74d86152a109560fd0ebe/Screen_Shot_2016-06-02_at_11.24.20.png)

See merge request !4435