Add `scrollFade` similar to `scrollShadow`

[techniq]

Using mask-image / -webkit-mask-image with a linear-gradient, fade content if scrollable, similar to scrollShadow. See REPL (without scroll adjustment like scrollShadow)

• [x] Ease in fade based on scroll amount (like scrollShadow)
• [ ] Enable/disable per side (use shadow for top, fade for bottom, for example)
• [ ] Support vertical and horizontal at same time (difficult with mask-image and linearGradient)

[techniq]

Create A Fade Out Overflow Effect Using CSS Mask-Image

[techniq]

https://twitter.com/johnphamous/status/1724491202148675590?s=46&t=NkyuWxqLoCUsNawsW7EzfA