Support gradient fills in inline vector icons

[markdumay]

Is your feature request related to a problem? Please describe.
The docs site used gradient fills to customize the styles of the referenced (Font Awesome) icons. However, with the introduction of inline vector graphics in release v0.17.0, the current CSS styles no longer work.

Describe the solution you'd like
Provide support to style inline vector graphics with custom gradients. The syntax of the SVG format is slightly different compared to web fonts, however, it can be linked to dynamic CSS variables (such as the color-mode aware Bootstrap theme colors).

Describe alternatives you've considered
N/A