body{background:#f5f5f5;font-family:system-ui,-apple-system,sans-serif;margin:0;padding:40px}.container{margin:0 auto;max-width:600px}.collapsible__button{background-color:#007bff;border:none;border-radius:8px;color:#fff;cursor:pointer;display:inline-block;font-size:18px;font-weight:500;padding:16px 20px;text-align:left;transition:background-color .2s}.collapsible__button:hover{background-color:#0056b3}.collapsible__content{max-height:0;opacity:0;overflow:hidden;transition:max-height 2s linear,opacity .2s ease-out,margin .2s ease-out}.collapsible__content.open{max-height:500px;opacity:1}.collapsible__text{background-color:#fff;border:1px solid #ddd;border-radius:8px;line-height:1.5;margin-top:8px;padding:20px}