Editing your theme CSS file (as detailed in this article) is not the preferred method for changing your theme style.
Instead, wherever possible, use the tools provided at your Aarcade admin area per How do I edit my theme's styles and options?
This article shows you where to add custom style code for your currently installed theme at your Big Cartel admin. To add custom style code to your saved theme files at your Aarcade admin, refer to the above-linked article.
Click the Customize design link in your Big Cartel admin area to launch your customisation tools.
Click the advanved icon and then click the CSS link:
Click the full screen icon:
Scroll to the very bottom of the CSS code and enter your custom style coding at the end of ALL existing code.
If there is already code in or after your CUSTOM SYLES section, scroll past it and always insert new code at the very bottom so that it becomes the last piece of code in your CSS file.
Always exit fullscreen mode, click the Done button and then the Save link after making any changes.
Note that our example above includes Theme custom styles in the CUSTOM STYLES area. For information on this, refer to The theme-specific custom styles
For more information on creating your own custom styles, refer to How do I create custom style code?.