Redesign "Edit in fullscreen" page's style

This is some suggestions for "Edit in fullscreen" page:

1. Add a light color border for text area or add a light background color except text area.
2. Keep text style unchanged : adjust text area's font-size, line-height etc.
3. Text area's width could be more wider. On my computer, screen is 19201080 px, but text area's width is only 900 px (include 302 px padding), less than half. I think the width could be 100%.