Accounts with a flat series (a single valuation or an unchanged balance, where
dataMin === dataMax) plotted the centered horizontal trendline at the full 2px
stroke — a near-black full-bleed rule bisecting the hero card in light, leaving
~half the card a void (dark read it as an acceptable hairline). Detect the flat
case (_isFlatSeries) and draw the line as a faint hairline (stroke-width 1,
stroke-opacity 0.4) so it reads as "no change", consistent across light + dark.
Verified on the Car Loan account (30D, no change): the heavy rule is gone.
Guillem Arias Fauste
6961c7ef41