fix OutfitPreview fade out bug

Oops, when switching to @emotion/react, it turns out they no longer support that cute hack I was doing to append suffixes to class names!

Here, I change strategy and let `CSSTransition` apply the plain `exit` and `exit-active` classes to its children, and apply Emotion styles to the child to check for _also_ having those classes.

src/app/components/OutfitPreview.js

@@ -100,7 +100,6 @@ export function OutfitLayers({
   loadingDelayMs = 500,
   spinnerVariant = "overlay",
   doTransitions = false,
-  onChangeHasAnimations = null,
   isPaused = true,
 }) {
   const containerRef = React.useRef(null);
@@ -177,19 +176,22 @@ export function OutfitLayers({
                 // We manage the fade-in and fade-out separately! The fade-out
                 // happens here, when the layer exits the DOM.
                 key={layer.id}
-                classNames={css`
-                  &-exit {
+                timeout={200}
+              >
+                <FadeInOnLoad
+                  as={FullScreenCenter}
+                  zIndex={layer.zone.depth}
+                  className={css`
+                    &.exit {
                       opacity: 1;
                     }
 
-                  &-exit-active {
+                    &.exit-active {
                       opacity: 0;
                       transition: opacity 0.2s;
                     }
                   `}
-                timeout={200}
                 >
-                <FadeInOnLoad as={FullScreenCenter} zIndex={layer.zone.depth}>
                   {layer.canvasMovieLibraryUrl ? (
                     <OutfitMovieLayer
                       libraryUrl={layer.canvasMovieLibraryUrl}