Rectangles with rounded corners are mathematically wrong. Once you know why, you can’t unsee it. Squircles, made iconic by Apple, are finally supported in browsers by the new CSS corner-shape: squircle property. I will show you how to approximate one squircle corner with just three pixel-perfect Bézier curves, so you can use squircles everywhere: canvas, SVG, clip-path, and even game engines. Your eyes deserve curves that actually make sense.
I agree. C2 continuity does matter for aesthetics sometimes, but not for a button.