Run the demo: create a key nobody holds, then sign with it
Sign in with an email address to get a one-time code, create a wallet whose private key is never assembled — four rounds of distributed key generation, reported as they happen — then sign a test transfer and read back what the coordinator understood it to be. Send one over the limit and it is held instead, with a cancellation link that arrives by email rather than in this tab. Nothing is broadcast to any network, no balance is real, and the address you type is used only to send you a code. What this is and why the key is split is on the description page.
About the dark panel
The signing panel is not part of this page. It is an iframe served from a different origin, and the browser's same-origin policy is what separates them: script running here cannot read its memory, its storage, or the share it holds. Only a structured message with a fixed set of shapes crosses between them. This page asks for a signature; it never asks for the share, because there is no message that would answer — which is what lets an application embed this wallet without being trusted with anything. The longer version is on the description page.