The `window-drag` CSS property allows web content to designate regions of an installed desktop web app’s UI that should behave as draggable window titlebar areas. When applied, user pointer interactions (e.g., click-and-drag) on that region move the top-level application window rather than triggering normal page interaction. This is primarily used by desktop PWAs or apps using features like Window Controls Overlay to implement custom title bars and draggable areas when the browser-provided title bar is hidden. This feature standardizes and renames the existing `app-region` CSS property, changes its value names to `move` and `none`, and adds explicit inheritance behavior. This property is used by installed web apps and Electron-based applications for the same purpose.
The CSS Working Group resolved to standardize the property under the name `window-drag` to better reflect its behavior. This feature adds support for the standardized `window-drag `property as a new CSS property in Chromium. Chromium is not deprecating or removing `app-region` or `-webkit-app-region`. Both legacy properties will remain fully supported. Internally, `app-region` is implemented as a surrogate that maps to `window-drag`, making this an additive change with no migration burden on existing content. Supporting the standardized name aligns Chromium with the CSSWG resolution while keeping the cost and risk minimal.