CSS & layoutGrid Lanes masonry settles on Grid syntax, and flow-tolerance is now fit-tolerance
A Piccalilli walkthrough by Saleh Mubashar traces native CSS masonry from its 2017 CSSWG issue to display: grid-lanes, and notes that the lane-picking property is now called fit-tolerance. Per the article, Grid Lanes works in Safari 26.4 and later, and support in other browsers is still evolving.