do you mean content width or what? Would be great if you can show us on screenshot how exactly you wish to do this and also please provide us link to such single post page.
To use above css on desktop versions only, you must wrap it into right @media screen tags. For more details about @media rules, we suggest to read http://www.w3schools.com/cssref/css3_pr_mediaquery.asp - also, you can check responsive.css files where @media rules are to check how to wrap the code. The css should be as below:
@media only screen and (min-width: 1240px) { .single-post #Content .sections_group { width: 70% !important; } }
Comments
do you mean content width or what? Would be great if you can show us on screenshot how exactly you wish to do this and also please provide us link to such single post page.
.single-post #Content .sections_group { width: 70% !important; }