Thank you very much and sorry for late reply. It went unanswered.
Front End is where your theme style file is loaded but in back end theme style file is not loaded. It is just for administrative purpose, style is not important here. In front end where users see their message and interact.
This plugin include basic style, most of the style come from theme to match with other parts of the website.
For multi-line, wordpress uses wpautop function which reduce line breaks and add p tags.