When the system layer gets created it toggles the icons inside vsync mutates. Adding the icons without user interaction will count as CLS to the system layer because it changes size, but we can fix it by giving it the initial size that fills the width so that adding icons will not generate CLS (tested on Chrome and the CLS disappears).

On desktop there is a CLS when on desktop panels because adding the desktop class happens on a vsync after adding the system layer to the shadow root. We need to initialize the desktop state (UI type classes) when the system layer is created, not after a vsync. Therefore we need to initialize the listener synchronously manually, and then use vsync when updating the UIType inside a vsync.

I found that these 2 fixes can improve CLS by 3% (0.03 CLS score) or more, which is 30% of the limit for CLS (0.1)