Allow SCSS variables to be overridden during library initialization

[notsure]

Currently, the SCSS variables defined in the library cannot be overridden from outside when the library is initialized.
This limits flexibility for consumers who need to customize styles (e.g. colors, spacing, breakpoints) without modifying the library source.

The task is to update the SCSS setup so that selected variables can be overridden externally at initialization time (e.g. via @use / @forward with !default values), while preserving sensible defaults within the library.

Acceptance criteria:

SCSS variables are defined in a way that allows external overrides

Default values remain intact when no overrides are provided

The approach follows best practices for modern SCSS usage

Documentation or examples are updated if necessary

Alternative (shorter & more direct)

Title:
Make SCSS variables configurable from outside the library

Description:
Expose library SCSS variables so they can be overridden by consuming projects during initialization, without requiring changes to the library’s source code.