Web viewport doesn't cover whole window

[jcs224]

This what happens when I try increasing the starting size of the window.

Following the example from the app, this is the only thing I changed:

const app = await launch({
  title: "Hello Deno!",
  width: 1280,
  height: 720,
});

Using Linux, POP!_OS, a Ubuntu derivative. Newest Chrome is installed on my system.