Child Theme

Do not edit any of the theme core files directly, as all your changes will be lost, when updating the theme. 

Use the Bricks child theme to add any custom code. You'll find a blank child theme within your Bricks account for download, named bricks-child.zip

Upload this child theme like any other WordPress theme. Go to Appearance > Themes and activate Bricks Child Theme. You can add your own styles to style.css.

To learn more about how to use a Child Theme have a look at the official WordPress Codex: http://codex.wordpress.org/Child_Themes
Quick note: The functions.php file of a child theme, unlike style.css, does not override the functions.php file of the parent theme. Instead, it is loaded in addition to the parent themes' functions.php, right before the parent file.