Gmail for desktop is testing a subtle tweak to its icons in a handful of spots, replacing the old filled-in icons with higher-contrast outlines. It's a minor tweak, and it's not live for everyone yet, but it finally brings the desktop web version of Gmail the icons that the Android app's been using for years.
Slide to see the difference
The change only affects icons for things like the sidebar folder navigation and the actions listed at the top of emails. The change replaces the older filled-in gray icons with slightly darker outlined versions, though the general look remains about the same and equally "Googly."
This change in iconography doesn't just match what Gmail's Android app has had for years, since its big nu-material redesign, it also matches changes Google has rolled out to Android and other apps in the last few years. These outline-style icons are the future, if you're Google, and they'll probably eventually replace any filled-in icons across all the company's apps and services.
The change doesn't seem to have hit everyone just yet. It could even be part of a limited test — literally billions of people use Gmail, and Google's going to be very tentative with any changes to it. Should it pass muster, expect to see the change roll out more widely.