Can I change the theme of the customer portal?

Yes, you can.
You you can change the theme and customize the customer portal by:

1. Defining the style of the portal in a CSS file
2. Pasting the CSS file URL in the customer portal setting

Follow these steps to insert the CSS file URL in the CRM:

1. Click the User Menu on the top right corner of the screen.
2. Click the Settings button.
3. Select Customer Portal under Configuration.
4. Paste the file URL in the CSS URL for Custom Theme field.
5. Click Save.