`svelte.dev` has FOUC

[sacrosanctic]

I noticed recently that www.svelte.dev is causing FOUC. I suspect it is the most recent update. It happens on my Android device, and I'm not sure how to document it.

[rChaoz]

Just tested a bit and on desktop the only thing I can get to flash is the alt of the hero image, even with no cache and slow internet emulation (Windows/Firefox & Chrome).

On Android/Firefox, loading the page after clearing the cookies/data does flash white to black, as the SSR cannot know my device theme beforehand. This does not happen if manually enabling the dark theme before loading the page.