No, please do not paste into Additional CSS – it is different code.
Please follow the guidance carefully.
1. Use child theme (you could find from main file downloaded from Themeforest), read here for detail: http://support.jegtheme.com/documentation/child-theme-3/
2. After upload & activating the child theme, go to Appearance > Editor. At the Theme Files section click the “Theme Functions” (functions.php)
3. Copy this code to the bottom of the Theme Functions (functions.php) :
4. Click Update File