Shown in the screenshot is the Canary branch of Chrome OS (the latest feature compiled version). The new theme not only covers the entire page area of the browser, but also takes into account the download folder, setting the toolbar and other areas.
Given Google’s commitment to "design consistency" across operating systems, we can anticipate the future from Chrome OS CanaryWindowsThe style when the version is finished.
Of course, there are subtle differences in the dark theme under different platforms. For example, text in Windows renders black in dark gray; in Chrome OS, it is grayed out to improve contrast.
Google is expected to officially launch a dark theme in the Chrome 75+ later this year.