“The icon is a static SVG image that’s about 3 lines of text.”
A spinning “build in progress” icon in Bitbucket pins a CPU core for as long as a build runs. Rotating it forces a full layout recalculation every frame. Rendering drops from 6 ms to 1 or 2 ms when the animation goes. Atlassian ships a three-line SVG that costs every developer half a core, and the developers pay the power bill.