The palette to use.
Takes effect immediately on widgets already on the page — it sets one attribute on the document element and the colours are custom properties, so nothing is rebuilt.
The default is 'dark', not 'auto', on purpose. These panels sit over a basemap, and the right
palette follows the MAP rather than the OS: light panels over dark satellite imagery read worse
than dark panels on a light-mode desktop. Pick to match your basemap; 'auto' is there for an
app whose basemap already follows the system.
Choose the widget palette:
'dark'(the default),'light', or'auto'to follow the operating system'sprefers-color-scheme.