:root{--white:#fff}
*{box-sizing:border-box;margin:0;padding:0}
html,body{height:100%}
body{background:var(--white);overflow:hidden}

.stage{min-height:100vh;display:grid;place-items:center}

.casque{max-width:min(80vw, 900px);max-height:80vh;opacity:0;transition:opacity 600ms ease-in-out}
.casque.is-visible{opacity:1}

/* Page transition overlay  (fade to white) */
.page-fade{position:fixed;inset:0;background:var(--white);opacity:0;pointer-events:none;z-index:9999;transition:opacity 200ms ease-in-out}
.page-fade.is-active{opacity:1}

@media (prefers-reduced-motion: reduce){
  .casque{transition:none}
  .page-fade{transition:none}
}