WordPress 4.7 introduced the Customize > Additional CSS tab. Any CSS code added to Customize > Additional CSS applies to any part of any page site-wide, whether it's in a Beaver Builder layout, in a theme area, in a WordPress content area, or a generated archive page.
The Additional CSS tab contents are theme-specific. If you activate a different theme, the CSS rules will disappear from the Additional CSS tab, but they'll reappear if you reactivate the theme in which you added the rules. If you have CSS rules in Additional CSS that you want to migrate to a new theme, copy the rules manually.
CSS rules placed in Additional CSS are stored in the database. See the article about where to put custom CSS.
Updating from old versions of Beaver Builder Theme
The Customize > Code > CSS Code tab was eliminated in Beaver Builder Theme Version 1.6.
If you update a Beaver Theme installation from a version earlier than 1.6, any CSS code stored in the old Code > CSS Code tab is automatically migrated to Customize > Additional CSS. The migrated code has the following comment to identify it:
CSS Migrated from BB theme:
If you import Beaver Builder Theme Customizer settings from a 1.5 .dat file into Beaver Builder Theme 1.6 or higher, CSS from the Customize > Code > CSS Code tab will automatically migrate to the Additional CSS tab.
If you export/import Beaver Builder Theme Customizer settings, CSS code in the Customize > Additional CSS tab currently will not export or import. Make sure to manually copy the CSS code from the old location to the new location if you want to move it.