A branding and marketing team wants to customize the theme in the externalcustomer support site...

To customize the theme in the external customer support site to match the style guide requirements, the recommended next step is to configure the Experience Builder Theme panel. The Theme panel allows the designer to customize the look and feel of the site by setting the logo, colors, fonts, and other branding elements. The designer can also create custom themes and assign them to different pages or audiences. The Theme panel is the preferred way to apply consistent branding across the site without writing any code or overriding any styles. References: : Theme Panel | Salesforce Help : UX Designer Certification Prep: Designing with Experience Builder | Trailhead