It's not easy, that's for sure. These days, big organizations tend to develop an internal "Design System" along with some implementations. Many of those design system implementations are, in fact, open, so you might just use those.

Example 1: Google has "Material Design". Here are some key resources:

1. Material Design Components (MDC):

- For Android: MDC-Android

- For iOS: MDC-iOS

- For Web: MDC-Web

2. Material Design for Flutter: A set of widgets implementing Material Design for Flutter apps.

3. Material-UI (MUI): While not created by Google, it's a popular React library that implements Material Design.

4. Material Theme Editor: A tool for creating and customizing Material themes.

5. Material Icons: Official Material Design icons.

6. Material Design Guidelines: Comprehensive documentation on implementing Material Design.

You can find these resources and more on the official Material Design website (material.io) or Google's developer documentation.

Example 2: Microsoft has "Fluent 2". Google it.

Example 3: The UK Government has the "GOV.UK Design System". See https://design-system.service.gov.uk/

Example 4: Adobe's official design system is called "Adobe Spectrum." Google it.