Try rotate3d instead

Got to squeeze out that GPU power yo

src/app.css

@@ -725,7 +725,7 @@ button.carousel-dot[disabled].active {
   transition: transform 0.3s ease-in-out;
 }
 #compose-button[hidden] .icon {
-  transform: rotateY(180deg);
+  transform: rotate3d(0, 1, 0, 180deg);
 }
 #compose-button:is(:hover, :focus) {
   background-color: var(--button-bg-color);