* refactor: add standardized spacing variables and more style cleanup
* refactor: rename `spacing-xxl` to `spacing-2xl` and introduce `spacing-3xl` for consistent spacing variables.
* refactor: Migrate related content styling to use the `subsection-list` component with updated layout adjustments.
* style: adjust padding values for article list tiles.
* refactor: Introduce shadow variables and dynamic spacing to prevent shadow cutoff in list layouts.
* refactor: relocate dark scheme Mermaid variables within the root scope.
