That’s great, but I’ve been able to do that with CSS for years.
It feels like there is a lot of brigading and shilling of Astro throughout this thread, as typical with web frontend frameworks.
Then why do you need bloated web UI that's not performant as React, Vue, Angular, Svelte? You can also just add 1 line of css classes to HTML elements to have transitions if you use a library like Animate.css.