The built-in theme provides a strong base that can be extended further for your requirements. For customization, the pass through values need to be overriden. The unstyled section of the theming documentation for each component demonstrates the theme with an editable example. For instance, the panel component has the following default configuration.
Let's assume the title section should be lighter and bigger. To begin with, clone the Tailwind theme to create your own, override the default values with your own utility classes and finally configure your own theme object as the pt of PrimeVue.