vivo Sans is a systematic font for smartphones created by vivo and FounderType. It contains 29,603 characters and is the first to adopt stroke-level Dynamic Optical Size technology. It achieves variable font adaptation through a series of innovative features, and regardless of the font size, each character can be presented clearly in the most optimal format, enhancing the legibility and readability of small-sized text. We have also reduced the thickness of crossing strokes so that the intersecting point is less likely to appear “over black” in small font sizes. Overall, vivo Sans provides mobile users with an intuitive and comfortable reading experience.