:root{
      --bg: linear-gradient(180deg,#f2f6ff,#eef4ff);
      --card: rgba(255,255,255,0.9);
      --muted: #6b7280;
      --accent: #6e8bff;
      --glass: rgba(255,255,255,0.6);
      --radius: 14px;
      --shadow: 0 10px 30px rgba(16,24,40,0.08);
      --accent-2: #24d5b2;
    }
    .dark{
      --bg: linear-gradient(180deg,#071026,#07182a);
      --card: rgba(12,18,30,0.6);
      --muted: #9aa4b2;
      --accent: #6ea8fe;
      --glass: rgba(255,255,255,0.03);
      --shadow: 0 10px 30px rgba(2,6,23,0.6);
      color: #e6eef8;
    }
    *{box-sizing:border-box}
    html,body{height:100%;margin:0;font-family:Inter, "Helvetica Neue", Arial, sans-serif;background:var(--bg);-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale}

    /* page layout */
    header{position:fixed;left:0;right:0;top:0;height:64px;padding:10px 22px;display:flex;align-items:center;justify-content:space-between;gap:12px;backdrop-filter:blur(8px);background:var(--glass);box-shadow:var(--shadow);z-index:60}
    .brand{display:flex;gap:12px;align-items:center}
    .title{font-weight:700;font-size:16px}
    .subtitle{font-size:12px;color:var(--muted)}

    .top-controls{display:flex;gap:8px;align-items:center}

    main{padding:86px 20px 110px;display:grid;grid-template-columns:320px 1fr;gap:18px;min-height:calc(100vh - 160px)}
    .sidebar{background:var(--card);border-radius:var(--radius);padding:14px;box-shadow:var(--shadow);overflow:auto}
    .panel{background:var(--card);border-radius:var(--radius);padding:12px;box-shadow:var(--shadow);}

    /* sidebar */
    .new-btn{width:100%;padding:10px;border-radius:10px;background:linear-gradient(90deg,var(--accent),#7ad6ff);color:#fff;border:0;font-weight:700;cursor:pointer}
    .controls-row{display:flex;gap:8px;margin-top:10px}
    .icon-btn{border:0;background:transparent;padding:8px;border-radius:10px;cursor:pointer;color:var(--muted)}
    .icon-btn:hover{background:rgba(0,0,0,0.04)}
    .section-title{font-size:12px;color:var(--muted);margin-top:12px;margin-bottom:8px;text-transform:uppercase;letter-spacing:0.6px}

    .conv-list{display:flex;flex-direction:column;gap:8px}
    .conv-item{display:flex;gap:10px;align-items:center;padding:10px;border-radius:10px;cursor:pointer;justify-content:space-between}
    .conv-item:hover{background:rgba(0,0,0,0.03)}

    /* chat area */
    .chat-area{display:flex;flex-direction:column;gap:12px;height:calc(100vh - 200px)}
    .messages{flex:1;overflow:auto;padding:18px;display:flex;flex-direction:column;gap:12px;border-radius:12px;background:linear-gradient(180deg,transparent,rgba(0,0,0,0.02))}
    .msg{max-width:78%;padding:14px;border-radius:12px;box-shadow:0 6px 18px rgba(2,6,23,0.04);line-height:1.6;position:relative}
    .msg.user{margin-left:auto;background:linear-gradient(90deg,var(--accent),#4895ef);color:#fff;border-bottom-right-radius:6px}
    .msg.ai{margin-right:auto;background:var(--card);color:inherit;border:1px solid rgba(0,0,0,0.04)}
    .meta{display:flex;gap:8px;align-items:center;font-size:12px;color:var(--muted);margin-bottom:8px}

    .msg .actions{position:absolute;right:8px;top:8px;display:flex;gap:6px}
    .badge{display:inline-block;padding:6px 8px;border-radius:999px;font-size:12px;background:rgba(0,0,0,0.04);color:var(--muted)}

    /* composer (悬浮) */
    .composer-wrap{position:fixed;left:50%;transform:translateX(-50%);bottom:18px;width:min(92%,1100px);display:flex;align-items:flex-end;justify-content:center;z-index:70}
    .composer{width:100%;display:flex;gap:12px;align-items:flex-end;padding:12px;border-radius:18px;background:linear-gradient(180deg,rgba(255,255,255,0.9),rgba(255,255,255,0.98));box-shadow:0 14px 50px rgba(16,24,40,0.12)}
    .composer.dark{background:linear-gradient(180deg, rgba(8,12,20,0.6), rgba(8,12,20,0.7))}
    textarea{flex:1;min-height:56px;max-height:240px;padding:12px;border-radius:12px;border:1px solid rgba(0,0,0,0.06);resize:none;font-size:14px}
    .send-btn{padding:12px 18px;border-radius:12px;border:0;background:linear-gradient(180deg,var(--accent),#2b9bff);color:#fff;font-weight:700;cursor:pointer}
    .mini-btn{padding:8px 10px;border-radius:10px;border:0;background:rgba(0,0,0,0.04);cursor:pointer}

    /* utilities */
    .small{font-size:12px;color:var(--muted)}
    .muted{color:var(--muted)}
    .hidden{display:none}

    /* responsive */
    @media(max-width:900px){
      main{grid-template-columns:1fr;padding-bottom:160px}
      .sidebar{order:2}
      .composer-wrap{bottom:10px}
    }
    /* small micro-interactions */
    .pulse{animation:pulse 1.6s infinite}
    @keyframes pulse{0%{transform:scale(1)}50%{transform:scale(1.02)}100%{transform:scale(1)}}