Two ways to customize, one of them is a trap
You can make PrimeNG match a brand two ways: override component internals with targeted CSS selectors, or configure PrimeUIX's token-based preset system to redefine the design tokens the components already read from. The first feels faster in the moment. The second is the one that survives a version upgrade.
CSS overrides target implementation details — internal class names, DOM structure — that PrimeNG doesn't guarantee stability on between versions. A token-based preset targets a documented, stable API surface instead.
A workflow that holds up
Start from the preset, not from Aura's defaults in place
Extend PrimeUIX's base preset (`definePreset`) with your palette from day one, rather than shipping the default theme and patching colors later across dozens of screens.
Map brand colors to semantic tokens, not component props
Set `primary`, `surface` and `formField` tokens once in the preset. Every button, input and card across the app inherits it — no per-component color prop to remember or miss.
Define light and dark variants in the same preset
PrimeUIX supports per-mode token values directly in the preset definition. Define both there rather than adding a separate `dark:` CSS override layer on top of the theme.
Reserve component-level `pt` (passthrough) props for real one-offs
PrimeNG's passthrough API is the correct escape hatch for a genuinely unique instance. If you're reaching for it on every instance of a component, the preset is missing a token.
Keep the preset in version control as its own module
Treat the theme preset as a first-class file a designer or engineer can review on its own, not scattered token overrides mixed into feature-level SCSS.
Re-test the preset on every major PrimeNG upgrade
Token names occasionally shift between major versions. A five-minute visual check of core components after upgrading catches this far cheaper than a support ticket weeks later.
Why this matters more than it looks like it should
A CSS-override-heavy theme accumulates silently. Each individual override looks harmless on its own PR, but two years in, upgrading PrimeNG becomes a project of its own — every overridden selector needs re-verification against the new DOM structure, and some will have quietly broken without anyone noticing until a user reports a visual bug.
A token-based preset doesn't eliminate that risk entirely, but it shrinks the surface area dramatically: a documented API instead of implementation details you were never meant to depend on.
The takeaway
Theme PrimeNG through PrimeUIX's token-based preset system, not CSS selectors chasing internal class names. Map brand colors to semantic tokens once, define light and dark in the same preset, and reserve passthrough props for genuine one-offs — and the next major-version upgrade becomes a five-minute visual check instead of a multi-week re-theming project.
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See this theming approach applied in production on the Compito case study.