Docs - how to customize global and component styles

Goal is to create documentation around how to customize patternfly styles. This would like cover something like:

Components

• Vars are the API for styling components. They're protected from breaking changes.
• Try to write all overrides like the following

.pf-v6-c-component {
  --pf-v6-c-component--BackgroundColor: var(--pf-t--global--[semantic color var]);
  --pf-v6-c-component__element--Gap: var(--pf-t-global--[semantic spacer var]);
  ...
}

• Be mindful of specificity/loading order
• Avoid writing out nested property styles with regular property declarations. If users need to do this, they should bring their override back to PF and we can consider adding vars to support it. If we don't add vars, suggest not making that kind of override.
• ...

Global/tokens

:where(:root) {
  --pf-t--global--[token]: var(--pf-t--global--[other token);
}

:where(.pf-v6-m-theme-dark) {
  // same as above but for dark theme
}

...
+ any other stuff that seems appropriate

No file, test, or documentation entry point is named; start by locating where PatternFly styling and token guidance belongs. Done means documenting component variable overrides, specificity and loading order, global and dark-theme token overrides, and when nested property overrides should be avoided or proposed as new variables.