The look of tab groups seems to have changed: In stock Chromium, the color line is solid across the bottom of the tabs, and bends around the active tab. In current Edge, this got changed to run across the top of the grouped tabs, which somehow just feels more intrusive and claustrophobic - having the color strip at the bottom feels more airy than the new style. The new style also looks frankly bad on the active tab, where the line breaks and shoots through the active tab. You could probably make something like that look good with a lot of animation and skeuomorphism to build the feel that the tabs are hanging on a thread and the thread goes through the tabs, but the old look's simpler and less cramped feeling.
