Created attachment 466478 [details] A demonstration of the bug See attached example bug.html The example contains a custom element my-element which contains a div with a background colour of red. This div has the following css selector :host(.makeGreen) div applied to it so when the custom element gets the makeGreen class, the div background turns from red to green. Click on the custom my-element in bug.html. This applies the makeGreen class to the custom element and therefore the background colour of the div inside the custom element should change from red to green. However, the background colour of the div inside the custom element remains red. It looks like the correct styling is being applied in the inspector but a redraw has not happened. Forcing a redraw, that is, uncommenting the code commented out in the bug.html results in the correct functionality. This bug is also observed not just with background-color but other properties such as object-fit. Observed on: Safari Version 16.5 (18615.2.9.11.4) on macOS Ventura 13.4 Safari Version 16.4 (18615.1.26.110.1) on macOS Ventura 13.3.1 (a) Safari Version 16.4.1 (16615.26.101.10 16615) on macOs Big Sur