changing the size of a page

When members log in to view their account page it is too wide and the link to edit their profile is off the page

I wrote about it here and was told to put some code in to the style.css file but that didn't work. Any ideas about where to add the code so the edit link shows up on the page?

Here is the link to the original post

https://premium.wpmudev.org/forums/topic/the-account-form-is-off-the-page

I need to add this code

div#account-form {
width: 90%;
}

thanks
Diane