*{margin:0;padding:0;box-sizing:border-box}
:root{
  --bg:#f0f2f5;--card:#fff;--primary:#1677ff;--primary-hover:#4096ff;
  --text:#1f1f1f;--text2:#666;--border:#e4e7ed;--shadow:0 2px 8px rgba(0,0,0,.08);
  --sidebar-bg:#fafafa;--sidebar-w:280px;--radius:12px;
  --msg-user:#1677ff;--msg-ai:#f5f5f5;
}
body{font-family:-apple-system,BlinkMacSystemFont,'Segoe UI','PingFang SC','Hiragino Sans GB','Microsoft YaHei',sans-serif;background:var(--bg);color:var(--text);height:100vh;overflow:hidden}

#app{display:flex;height:100vh}

/* Sidebar */
#sidebar{position:fixed;left:0;top:0;width:var(--sidebar-w);height:100%;background:var(--sidebar-bg);border-right:1px solid var(--border);display:flex;flex-direction:column;z-index:100;transition:transform .3s ease;box-shadow:2px 0 8px rgba(0,0,0,.04)}
#sidebar.collapsed{transform:translateX(calc(-1 * var(--sidebar-w)))}
.sidebar-header{padding:12px;border-bottom:1px solid var(--border)}
.btn-new{width:100%;padding:10px;border:1px dashed var(--primary);border-radius:8px;background:var(--card);color:var(--primary);cursor:pointer;font-size:14px;transition:.2s}
.btn-new:hover{background:#e6f4ff}
.sidebar-body{flex:1;overflow-y:auto;padding:8px}
.session-item{position:relative;padding:10px 12px;margin-bottom:4px;border-radius:8px;cursor:pointer;transition:.15s}
.session-item:hover{background:#f0f0f0}
.session-item.active{background:#e6f4ff;color:var(--primary)}
.session-title{font-size:14px;overflow:hidden;text-overflow:ellipsis;white-space:nowrap;padding-right:20px}
.session-meta{font-size:11px;color:var(--text2);margin-top:2px}
.session-del{position:absolute;right:8px;top:8px;width:20px;height:20px;border-radius:50%;display:flex;align-items:center;justify-content:center;color:var(--text2);font-size:16px;opacity:0;transition:.2s}
.session-item:hover .session-del{opacity:1}
.session-del:hover{color:#ff4d4f;background:#fef0ef}
.sidebar-footer{padding:12px;border-top:1px solid var(--border)}
.btn-user{width:100%;padding:8px;border:1px solid var(--border);border-radius:8px;background:var(--card);cursor:pointer;font-size:13px}

/* Main */
#main{flex:1;display:flex;flex-direction:column;margin-left:var(--sidebar-w);transition:margin-left .3s ease;min-width:0}
#main.expanded{margin-left:0}
#chatHeader{display:flex;align-items:center;padding:12px 20px;border-bottom:1px solid var(--border);background:var(--card);gap:12px}
.menu-toggle{background:none;border:none;font-size:22px;cursor:pointer;padding:4px;line-height:1}
#chatTitle{font-size:16px;font-weight:600;flex:1}
.quota-badge{font-size:12px;color:var(--primary);background:#e6f4ff;padding:3px 10px;border-radius:20px}

/* Messages */
.messages{flex:1;overflow-y:auto;padding:20px;scroll-behavior:smooth}
.welcome{text-align:center;padding:60px 20px 40px}
.welcome-icon{font-size:64px;margin-bottom:16px}
.welcome h2{font-size:28px;margin-bottom:8px}
.welcome-sub{color:var(--text2);font-size:15px;margin-bottom:24px}
.welcome-tips{display:grid;grid-template-columns:repeat(auto-fit,minmax(140px,1fr));gap:10px;max-width:600px;margin:0 auto}
.tip{padding:12px 16px;border-radius:10px;background:var(--card);border:1px solid var(--border);cursor:pointer;font-size:13px;transition:.2s;text-align:center}
.tip:hover{border-color:var(--primary);color:var(--primary);transform:translateY(-1px);box-shadow:var(--shadow)}

/* Message */
.msg{display:flex;gap:12px;margin-bottom:20px;max-width:800px}
.msg-user{flex-direction:row-reverse;margin-left:auto}
.msg-avatar{width:36px;height:36px;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:18px;flex-shrink:0}
.msg-user .msg-avatar{background:var(--primary);color:#fff;font-size:16px}
.msg-ai .msg-avatar{background:#e8e8e8;font-size:18px}
.msg-content{padding:12px 16px;border-radius:var(--radius);line-height:1.7;font-size:14px;word-break:break-word}
.msg-user .msg-content{background:var(--primary);color:#fff;border-radius:18px 4px 18px 18px}
.msg-ai .msg-content{background:var(--card);border:1px solid var(--border);border-radius:4px 18px 18px 18px;min-width:50px}
.msg-content pre{background:#1e1e1e;color:#d4d4d4;padding:14px;border-radius:8px;overflow-x:auto;margin:8px 0;font-size:13px;line-height:1.5}
.msg-content code{background:#f0f0f0;padding:2px 6px;border-radius:4px;font-size:13px}
.msg-content pre code{background:none;padding:0}
.msg-content ul{padding-left:20px;margin:6px 0}
.msg-content li{margin:3px 0}
.loading-msg{text-align:center;padding:40px;color:var(--text2)}

/* Input */
.input-area{display:flex;gap:8px;padding:12px 20px 20px;background:var(--card);border-top:1px solid var(--border)}
.input-area textarea{flex:1;padding:10px 14px;border:1px solid var(--border);border-radius:10px;resize:none;font-size:14px;outline:none;line-height:1.5;max-height:200px;transition:border-color .2s}
.input-area textarea:focus{border-color:var(--primary)}
#sendBtn{padding:10px 24px;border:none;border-radius:10px;background:var(--primary);color:#fff;font-size:14px;cursor:pointer;transition:.2s;align-self:flex-end}
#sendBtn:hover:not(:disabled){background:var(--primary-hover)}
#sendBtn:disabled{opacity:.4;cursor:not-allowed}

/* Modal */
.modal{display:none;position:fixed;top:0;left:0;width:100%;height:100%;background:rgba(0,0,0,.4);backdrop-filter:blur(4px);z-index:999;align-items:center;justify-content:center}
.modal-content{background:var(--card);border-radius:16px;padding:28px;width:400px;max-width:90vw;max-height:90vh;overflow-y:auto;position:relative}
.modal-close{position:absolute;right:16px;top:12px;font-size:24px;cursor:pointer;color:var(--text2)}
.modal h3{font-size:20px;margin-bottom:16px;text-align:center}
.tab-bar{display:flex;margin-bottom:16px;border-bottom:1px solid var(--border)}
.tab{flex:1;padding:8px;border:none;background:none;cursor:pointer;font-size:14px;color:var(--text2);border-bottom:2px solid transparent}
.tab.active{color:var(--primary);border-bottom-color:var(--primary)}
.form-input{width:100%;padding:10px 14px;border:1px solid var(--border);border-radius:8px;margin-bottom:10px;font-size:14px;outline:none}
.form-input:focus{border-color:var(--primary)}
.auth-msg{color:#ff4d4f;font-size:13px;margin-bottom:8px;min-height:18px}
.btn-primary{background:var(--primary);color:#fff;border:none;padding:10px 0;border-radius:8px;cursor:pointer;font-size:14px;transition:.2s}
.btn-primary:hover{background:var(--primary-hover)}
.btn-full{width:100%}
.plan-list{display:flex;flex-direction:column;gap:12px}
.plan-card{border:1px solid var(--border);border-radius:12px;padding:16px;text-align:center}
.plan-card:hover{border-color:var(--primary)}
.plan-name{font-size:16px;font-weight:600;margin-bottom:4px}
.plan-price{font-size:28px;color:var(--primary);font-weight:700;margin:8px 0}
.plan-desc{font-size:13px;color:var(--text2);margin-bottom:12px}

/* Mobile */
@media(max-width:768px){
  #sidebar{width:85%;box-shadow:2px 0 20px rgba(0,0,0,.15)}
  #sidebar.collapsed{transform:translateX(-100%)}
  #main{margin-left:0}
  #main.expanded{margin-left:0}
  .welcome{padding:30px 12px 20px}
  .msg{max-width:100%;gap:8px}
  .msg-content{font-size:14px;padding:10px 14px}
  .input-area{padding:10px 12px 16px}
}