This outline approach makes the icons less likely to stand out on a busy page, which is both a good and bad thing, depending on the design objective. While lighter, they also look more generic.

These outline-style icons are not yet widely rolled out, but appearing for more YouTube Music Android users today following a server-side update. Try force stopping the application and reopening.

A thread of new tweets has recently appeared on the official Twitter design account. These new icons come with a thicker outline and now they don’t have angular shapes.