See the results of the following tests: imported/w3c/web-platform-tests/css/css-backgrounds/background-size/vector/tall--contain--height.html [ ImageOnlyFailure ] imported/w3c/web-platform-tests/css/css-backgrounds/background-size/vector/tall--contain--width.html [ ImageOnlyFailure ] imported/w3c/web-platform-tests/css/css-backgrounds/background-size/vector/wide--contain--height.html [ ImageOnlyFailure ] imported/w3c/web-platform-tests/css/css-backgrounds/background-size/vector/wide--contain--width.html [ ImageOnlyFailure ] They reference a background-image that is SVG with only one dimension, but with correct (if weird) proportions. According to CSS, their intrinsic size should be scaled down to provide the other dimension. We're not doing that.
<rdar://problem/67112504>
See also webkit.org/b/206753