:root{
  --bg:#f7f8fa;
  --sidebar:#ffffff;
  --accent:#2f80ed;
  --muted:#6b7280;
  --card:#fff;
  --border:#e6e9ef;
}

*{box-sizing:border-box}
html,body,#app{height:100%;margin:0;font-family:Inter,system-ui,-apple-system,Segoe UI,Roboto,"Helvetica Neue",Arial}
#app{display:flex;height:100vh;background:var(--bg);}

/* Sidebar */
#sidebar{width:300px;background:var(--sidebar);border-right:1px solid var(--border);display:flex;flex-direction:column}
.sidebar-header{display:flex;align-items:center;justify-content:space-between;padding:12px 14px;border-bottom:1px solid var(--border)}
.sidebar-header h1{margin:0;font-size:1.05rem}
#btn-new-chat{background:var(--accent);border:none;color:#fff;padding:6px 10px;border-radius:6px;cursor:pointer}
.search{padding:10px}
.search input{width:100%;padding:8px;border:1px solid var(--border);border-radius:6px}
#chats-list{list-style:none;margin:0;padding:0;overflow:auto;flex:1}
#chats-list li{padding:12px 14px;border-bottom:1px solid var(--border);cursor:pointer;display:flex;justify-content:space-between;align-items:center}
#chats-list li.active{background:linear-gradient(90deg,rgba(47,128,237,.08),transparent)}

/* Chat area */
#chat-area{flex:1;display:flex;flex-direction:column}
#chat-header{padding:12px 16px;border-bottom:1px solid var(--border);display:flex;justify-content:space-between;align-items:center}
#messages{flex:1;overflow:auto;padding:16px;display:flex;flex-direction:column;gap:8px;background:linear-gradient(180deg,#fff, #f7fbff 40%)}
.msg{max-width:70%;padding:8px 10px;border-radius:10px;border:1px solid var(--border);background:var(--card)}
.msg.me{margin-left:auto;background:linear-gradient(180deg,var(--accent),#2b6fe4);color:#fff;border:0}
.msg .meta{font-size:11px;color:var(--muted);margin-top:6px}
#message-form{display:flex;gap:8px;padding:12px;border-top:1px solid var(--border);align-items:center}
#message-input{flex:1;padding:10px;border:1px solid var(--border);border-radius:8px}

/* sidepanel */
#sidepanel{width:260px;border-left:1px solid var(--border);background:var(--sidebar);padding:12px}

/* modal */
#modal-overlay.modal-hidden{display:none}
#modal-overlay{position:fixed;inset:0;background:rgba(0,0,0,.35);display:flex;align-items:center;justify-content:center}
#modal{background:#fff;padding:18px;border-radius:8px;min-width:320px;position:relative}
#modal-close{position:absolute;right:6px;top:6px;border:0;background:transparent;font-size:18px;cursor:pointer}