(Note: based on the reftest-analyzer visualization at wpt.fyi, it looks like we might be avoiding this issue there for some reason, perhaps due to the system theme that the test-runner is using. But I do see it when I view the test locally on Linux, as well as on Windows.) The attached screenshot shows the wpt.fyi visulization of the failure on top (with opaque gray scrollbars that aren't flagged as mismatches between test/reference), and my own local rendering of the testcase on the bottom (with red scrollbars due to the fact that they're transparent for me and there's a red background behind them).
Bug 1702845 Comment 1 Edit History
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(Note: based on the reftest-analyzer visualization at wpt.fyi, it looks like we might be avoiding this issue there for some reason, perhaps due to the system theme that the test-runner is using, which perhaps imposes opaque scrollbars as the test is expecting. But I do see the issue when I view the test locally on Linux, as well as on Windows.) The attached screenshot shows the wpt.fyi visulization of the failure on top (with opaque gray scrollbars that aren't flagged as mismatches between test/reference), and my own local rendering of the testcase on the bottom (with red scrollbars due to the fact that they're transparent for me and there's a red background behind them).