The "Show All" button next to the reading list on the Start page does not change color depending on theme changes and blends in with the dark background.
Orion, OS version; hardware type:
MacBook Pro (13", 2017)
macOS Monterey 12.3 (21E230)
Orion 0.99.113.2-beta (WebKit 613.1.12)
Image/Video: