A few months ago Google was testing out a green search category navigation bubbles-shaped button in the mobile search results and now there are some reports suggesting that Google is testing out that button in several colors like green, orange, gray, and many more. Google is also working on the shape of the button by displaying the button as a square versus oval shape.
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You can see the screenshot below of how the square-shaped button looks like-
Screenshot of the colored oval buttons-
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