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Comment by reddalo | Hacker News Reader

I don't trust this article. Rotation of elements in CSS doesn't cause a reflow of the page, since it's a transform property, and so it doesn't cause a re-render like the article says.

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The article is wrong but the observations are correct. The codepen link posted somewhere downthread does result in usually high cpu usage (Chrome M2 Mac).

I trust them that Atlassian product performance is bad in ways that are always novel and surprising, at least.

Rotation of elements in CSS shouldn't cause a reflow of the page. But the devil is in the details and sometimes, with a deeply complicated declarative API for plotting content on screen, It's easy for the developers working on the browser's rendering layer to inadvertently forget to do the correct thing in favor of the safe thing (ie if recalculating the layout ends up being the identity function, will testing actually pick up that the recalculation was in fact unnecessary or off spec?).

I have definitely in the past chased around a massive repaint bug that only showed up in Firefox using flex boxes (only to have it vanish at the next minor revision).

Since this performance hit is showing up in Chrome, it will be interesting to see if it is a Chrome specific issue or a webkit issue.

The reflow hypothesis can be confirmed by setting a fixed height and width on the icon and overflow: hidden.

this blog has a history of "interesting" takes

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