Adjust the two stops that match QuickCopy.css: solid black holds until the first
percentage, then the mask fades to transparent by the second. Hover the preview row (or use
“Always show mask”) to see the icon slot like in the app.
Keep “Solid through” < “Fade by” so the gradient makes sense (otherwise the mask can invert oddly).
Replace the two percentages inside .root:hover .textContent (and the copied / focus-within rules use the same values).