You just add/edit your styles in the browser and copy it to your css file once it's correct.
You really ought to try the LiveReload plugin for Chrome or FF. Then you can edit your CSS in Sublime instead and see the changes in real time in your browser.
Use a tool like LiveReload or similar and all your HTML/CSS changes show up in real time as you make and save them in your text editor (Sublime Text for example). Put your text editor on one screen and your website in a browser on another and you're good to go.