Switching to No sidebar make my comment field narrower on Mobile

When i Switching to No sidebar layout this affect my comment field narrower on Mobile and make it resized I want comment field to look like this on mobile with no sidebar layout https://dl.dropboxusercontent.com/u/7588358/File%2015-01-2017%2C%2018%2003%2024.png Now when i switch to No sidebar layout this affect my comment field and get this on mobile, really uncomfortable for end users. https://dl.dropboxusercontent.com/u/7588358/File%2015-01-2017%2C%2018%2003%2006.png Please help me to this issue!