Remember to go through the whole website and update the "clientid=XXXXX" to match your client's IDX or some of the modules will not render correctly.
Update Custom CSS
Next, you need to update the custom CSS in the client's IDX account.
Log in to the IDX admin panel, locate the client, and then select the "Control Panel" button to access the account.
Select the Setup tab > Design & Branding > CSS.
Copy the code (in the file attached to this article) in the area labeled "Add Code to Page Head".
Select "Save Changes".