/* ===== Reset ===== */
*,*::before,*::after{margin:0;padding:0;box-sizing:border-box}
html,body{height:100%}
body{
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei","Noto Sans TC",sans-serif;
  background:var(--t-bg);color:var(--t-text);
  display:flex;height:100vh;height:100dvh;overflow:hidden;
}

/* ===== 5 Themes × 12 CSS Variables ===== */
body[data-app-theme="dark"]{
  --t-bg:#0b0818;--t-side:#100b22;--t-card:#0d0a1c;--t-input:#151030;
  --t-border:#2b2350;--t-text:#f0eafc;--t-muted:#b0a3d6;--t-acc:#6d4fc2;
  --t-acc2:#4d357f;--t-accText:#fff;--t-ghost:#d4c8f5;--t-ghostBd:#5d4f96;
}
body[data-app-theme="black"]{
  --t-bg:#050505;--t-side:#0b0b0b;--t-card:#121212;--t-input:#1b1b1b;
  --t-border:#2d2d2d;--t-text:#f2f2f2;--t-muted:#bdbdbd;--t-acc:#6e6e6e;
  --t-acc2:#3a3a3a;--t-accText:#fff;--t-ghost:#dedede;--t-ghostBd:#666666;
}
body[data-app-theme="navy"]{
  --t-bg:#071120;--t-side:#0b1a30;--t-card:#0d1e38;--t-input:#112848;
  --t-border:#1f3d63;--t-text:#e8f1fc;--t-muted:#a8c0de;--t-acc:#2f6fd0;
  --t-acc2:#1d4c96;--t-accText:#fff;--t-ghost:#cbdef5;--t-ghostBd:#3c6aa5;
}
body[data-app-theme="light"]{
  --t-bg:#f6f1e7;--t-side:#eee7d7;--t-card:#fffdf6;--t-input:#ffffff;
  --t-border:#d8ceb7;--t-text:#2e2519;--t-muted:#6f5f45;--t-acc:#b3823f;
  --t-acc2:#8a5f26;--t-accText:#fff;--t-ghost:#5d4c30;--t-ghostBd:#b09a68;
}
body[data-app-theme="bamboo"]{
  --t-bg:#091309;--t-side:#0d1d10;--t-card:#102415;--t-input:#143020;
  --t-border:#24462f;--t-text:#eaf6ec;--t-muted:#a8ccb4;--t-acc:#37985c;
  --t-acc2:#23663e;--t-accText:#fff;--t-ghost:#cdead6;--t-ghostBd:#3d7a52;
}

/* ===== Scrollbars ===== */
#history-list::-webkit-scrollbar,
#thread::-webkit-scrollbar{width:6px}
#history-list::-webkit-scrollbar-thumb,
#thread::-webkit-scrollbar-thumb{background:var(--t-border);border-radius:3px}
#history-list::-webkit-scrollbar-track,
#thread::-webkit-scrollbar-track{background:transparent}

/* ===== Sidebar ===== */
#sidebar{
  display:none;width:264px;background:var(--t-side);
  flex-direction:column;border-right:1px solid var(--t-border);flex-shrink:0;
}
body.logged-in #sidebar{display:flex}

#sidebar-backdrop{
  display:none;position:fixed;inset:0;background:rgba(0,0,0,.4);z-index:25;
}
#sidebar-backdrop.open{display:block}

#btn-new-chat{
  display:flex;align-items:center;justify-content:center;
  margin:12px;padding:10px 0;border-radius:10px;
  border:1px dashed var(--t-border);background:transparent;
  color:var(--t-text);font-size:14px;cursor:pointer;
  font-family:inherit;transition:border-color .2s,background .2s;
}
#btn-new-chat:hover{border-color:var(--t-acc);background:var(--t-card)}

.sidebar-label{
  padding:12px 16px 4px;font-size:12px;color:var(--t-muted);letter-spacing:.05em;
}

#history-list{flex:1;overflow-y:auto;padding:4px 0}

.hist-item{
  padding:10px 12px;cursor:pointer;border-radius:8px;margin:2px 8px;
  font-size:14px;color:var(--t-text);display:flex;align-items:center;gap:8px;
  transition:background .15s;
}
.hist-item:hover{background:var(--t-card)}
.hist-item.active{background:var(--t-card);outline:1px solid var(--t-border)}
.hist-title{flex:1;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.hist-del{
  background:none;border:none;color:var(--t-muted);cursor:pointer;
  font-size:12px;padding:2px 6px;border-radius:4px;opacity:0;transition:opacity .15s;
}
.hist-item:hover .hist-del{opacity:1}
.hist-del.confirm{color:#ff6b6b;opacity:1}

#account-area{
  padding:12px 16px;border-top:1px solid var(--t-border);
  display:flex;align-items:center;gap:8px;margin-top:auto;
}
#user-display{
  flex:1;font-size:14px;color:var(--t-text);
  overflow:hidden;text-overflow:ellipsis;white-space:nowrap;
}
#btn-logout{
  background:transparent;border:1px solid var(--t-border);border-radius:8px;
  color:var(--t-muted);padding:4px 10px;font-size:12px;cursor:pointer;
  font-family:inherit;transition:border-color .2s,color .2s;
}
#btn-logout:hover{border-color:var(--t-acc);color:var(--t-text)}

/* ===== Main Area ===== */
#main-area{
  flex:1;min-width:0;display:flex;flex-direction:column;
  overflow:hidden;background:var(--t-bg);
}

/* ===== Topbar ===== */
#topbar{
  display:flex;align-items:center;padding:10px 16px;
  border-bottom:1px solid var(--t-border);gap:8px;flex-shrink:0;
}
#btn-menu{
  display:none;background:none;border:none;color:var(--t-text);
  font-size:20px;cursor:pointer;padding:4px;
}
#topbar-title{
  flex:1;font-size:16px;font-weight:600;color:var(--t-text);
  overflow:hidden;text-overflow:ellipsis;white-space:nowrap;
}
.topbar-right{position:relative;flex-shrink:0}
#btn-theme{background:none;border:none;font-size:18px;cursor:pointer;padding:4px 6px}

#theme-menu{
  display:none;position:absolute;top:calc(100% + 6px);right:0;
  background:var(--t-card);border:1px solid var(--t-border);border-radius:10px;
  padding:6px;z-index:50;min-width:120px;box-shadow:0 4px 16px rgba(0,0,0,.35);
}
#theme-menu.open{display:block}
#theme-menu button{
  display:block;width:100%;text-align:left;background:transparent;border:none;
  padding:8px 12px;border-radius:6px;color:var(--t-text);font-size:14px;
  cursor:pointer;font-family:inherit;transition:background .15s;
}
#theme-menu button:hover{background:var(--t-input)}

/* ===== Auth Screen ===== */
#auth-screen{
  flex:1;display:flex;justify-content:center;align-items:center;padding:20px;
}
body.logged-in #auth-screen{display:none}

#login-card{
  background:var(--t-card);border:1px solid var(--t-border);border-radius:16px;
  padding:32px;width:360px;max-width:90vw;
  display:flex;flex-direction:column;gap:14px;
}
.login-title{font-size:28px;text-align:center;color:var(--t-text);font-weight:700}
.login-sub{font-size:14px;text-align:center;color:var(--t-muted);line-height:1.6}

#login-card input{
  background:var(--t-input);border:1px solid var(--t-border);border-radius:10px;
  padding:10px 14px;font-size:15px;color:var(--t-text);outline:none;font-family:inherit;
}
#login-card input:focus{border-color:var(--t-acc)}
#login-card input::placeholder{color:var(--t-muted)}

#auth-error{color:#ff6b6b;font-size:13px;min-height:0;text-align:center}
body[data-app-theme="light"] #auth-error{color:#c0392b}

.auth-btns{display:flex;gap:10px}
.auth-btns button{
  flex:1;padding:10px;border-radius:10px;font-size:15px;
  cursor:pointer;font-family:inherit;transition:opacity .2s;
}
.auth-btns button:hover{opacity:.85}
#btn-login{background:var(--t-acc);color:var(--t-accText);border:none}
#btn-register{background:transparent;border:1px solid var(--t-ghostBd);color:var(--t-ghost)}

/* ===== Welcome Screen ===== */
#welcome-screen{
  display:none;flex:1;flex-direction:column;
  justify-content:center;align-items:center;gap:16px;padding:40px 20px;
}
.welcome-title{font-size:32px;color:var(--t-text);font-weight:700}
.welcome-sub{font-size:16px;color:var(--t-muted);text-align:center;line-height:1.6}

#welcome-chips{
  display:flex;flex-wrap:wrap;gap:10px;justify-content:center;margin-top:12px;
}
.chip{
  background:var(--t-card);border:1px solid var(--t-border);border-radius:20px;
  color:var(--t-ghost);padding:10px 18px;cursor:pointer;font-size:14px;
  font-family:inherit;transition:border-color .2s,background .2s;
}
.chip:hover{border-color:var(--t-acc);background:var(--t-input)}

/* ===== Thread ===== */
#thread{
  display:none;flex:1;overflow-y:auto;
  padding:18px max(16px,calc((100% - 900px)/2)) 24px;
  flex-direction:column;gap:16px;
}

.msg{margin:0;padding:0}

.msg-user{display:flex;justify-content:flex-end}
.msg-user .msg-bubble{
  background:linear-gradient(135deg,var(--t-acc),var(--t-acc2));
  color:var(--t-accText);border-radius:18px;padding:10px 16px;
  max-width:86%;font-size:15px;line-height:1.8;word-break:break-word;
}

.msg-assistant{padding:4px 0}
.msg-assistant .msg-plain{
  font-size:15.5px;line-height:1.95;color:var(--t-text);word-break:break-word;
}
.msg-assistant.streaming .msg-plain::after{
  content:'▌';color:var(--t-acc);animation:cursor-blink 1s steps(1) infinite;
}
@keyframes cursor-blink{50%{opacity:0}}

.msg-tech{margin-top:10px}
.msg-tech summary{
  cursor:pointer;color:var(--t-muted);font-size:12px;padding:4px 0;
}
.details-body{
  font-size:12px;line-height:1.7;color:var(--t-muted);
  margin-top:6px;padding:8px 0 8px 12px;border-left:2px solid var(--t-border);
  word-break:break-word;
}

.branch-hint{
  margin-top:12px;padding:8px 12px;border-left:2px solid var(--t-acc2);
  font-size:12.5px;line-height:1.8;color:var(--t-muted);
}

/* ===== Input Area ===== */
#input-area{
  display:none;flex-direction:column;flex-shrink:0;
  padding:8px max(16px,calc((100% - 900px)/2)) 16px;
  border-top:1px solid var(--t-border);
}
body.logged-in #input-area{display:flex}

#method-tabs{display:flex;gap:8px;padding:4px 0 8px}
.mtab{
  background:transparent;border:1px solid var(--t-border);border-radius:16px;
  color:var(--t-muted);padding:6px 14px;cursor:pointer;font-size:13px;
  font-family:inherit;transition:all .2s;text-align:center;
}
.mtab.active{background:var(--t-acc);color:var(--t-accText);border-color:var(--t-acc)}
.mtab-sub{display:block;font-size:11px;opacity:.7;margin-top:2px}

#status-bar{
  display:none;font-size:13px;color:var(--t-muted);padding:4px 0;line-height:1.5;
}
#error-bar{
  display:none;margin:4px 0;padding:8px 14px;
  background:rgba(194,80,79,.12);border:1px solid rgba(194,80,79,.35);
  border-radius:8px;color:#ff9f9f;font-size:13px;line-height:1.6;
}
body[data-app-theme="light"] #error-bar{
  color:#c0392b;background:rgba(192,57,43,.08);border-color:rgba(192,57,43,.25);
}

#input-row{display:flex;gap:8px;align-items:flex-end}

#user-input{
  flex:1;background:var(--t-input);border:1px solid var(--t-border);
  border-radius:12px;padding:10px 14px;font-size:15px;color:var(--t-text);
  resize:none;outline:none;font-family:inherit;line-height:1.6;max-height:150px;
}
#user-input:focus{border-color:var(--t-acc)}
#user-input::placeholder{color:var(--t-muted)}
#user-input:disabled{opacity:.5}

#send-group{display:flex;gap:6px;align-items:flex-end;flex-shrink:0}
#send-group button{
  border:none;border-radius:12px;padding:10px 16px;cursor:pointer;
  font-size:14px;white-space:nowrap;font-family:inherit;transition:opacity .2s;
}
#send-group button:hover{opacity:.85}
#send-group button:disabled{opacity:.4;cursor:not-allowed}
#btn-send,#btn-continue{background:var(--t-acc);color:var(--t-accText)}
#btn-new-q{background:transparent;border:1px solid var(--t-ghostBd) !important;color:var(--t-ghost)}

/* ===== Responsive ≤720px ===== */
@media(max-width:720px){
  body.logged-in #sidebar{
    position:fixed;top:0;bottom:0;left:0;z-index:30;
    transform:translateX(-100%);transition:transform .3s ease;
  }
  body.logged-in #sidebar.open{transform:translateX(0)}
  body.logged-in #btn-menu{display:inline-flex}

  #topbar{padding:10px 12px}

  #auth-screen{align-items:flex-end;padding:0}
  #login-card{
    width:100%;max-width:100%;border-radius:20px 20px 0 0;
    padding:28px 24px;animation:sheet-up .3s ease;
  }
  @keyframes sheet-up{from{transform:translateY(40%);opacity:0}to{transform:translateY(0);opacity:1}}

  #thread{padding:14px 12px 20px}
  #input-area{padding:8px 12px 12px}

  #input-row{flex-direction:column;align-items:stretch}
  #send-group{flex-direction:row;flex-wrap:wrap}
  #send-group button{flex:1 1 45%}

  .welcome-title{font-size:24px}
  .welcome-sub{font-size:14px}
  #welcome-chips{flex-direction:column;align-items:stretch}
  .chip{text-align:center}
}