Google recently updated the design of the search bar and activity status indicator in Gmail on the web. The search bar in Gmail on the web is now housed in a pill-shaped container. It used to be a rectangle with rounded corners, but the new design matches other Google web experiences like Google Drive and Search. It also matches the search bar in Gmail for Android.
In the meantime, the activity switcher, which was already in a pill, transitions from a button with a thin grey outline to a button that only uses colour. This change makes it more noticeable and distracting on dark themes because it appears enabled/actively highlighted. On the default light theme with a blue accent, it’s less noticeable.