What theme are you using. In general, you shouldn’t change theme files, but rather ADD CSS to make changes using a custom CSS option or plugin or child theme.
i’m using tango. hmm, okay so i should go to the “start here” css page then and just add my own stuff. i’ll try that. thanks.
I’d also suggest you ask the developer of the theme about this as he/she will be able to tell you the best way to make changes to your particular theme –
http://themeforest.net/item/tango-bootstrap-responsive-html5-wordpress-theme/4884066