Each side shorthand sets two corner radii. Before the slash are the horizontal radii; after the slash are the vertical radii. One value per side repeats for both corners. Logical sides follow writing-mode and direction.
Specification · WebKit bug · WebKit patch
Blink implementation: CL 7818574 (in review). The shorthands are behind an experimental, default-off flag: --enable-blink-features=CSSBorderRadiusSideShorthands.
Expected images use equivalent corner longhands; Diff compares the default-off browser with those images. Rendered is live in your browser. These are static baselines, not pixel comparisons against your browser.
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