:root{
  --bg:#f6f7f9; --card:#fff; --ink:#1a1d21; --muted:#6b7280; --line:#e5e7eb;
  --brand:#2563eb; --brand-dark:#1d4ed8; --ok:#059669; --err:#dc2626; --radius:12px;
}
*{box-sizing:border-box}
body{margin:0;font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"PingFang SC","Microsoft YaHei",sans-serif;background:var(--bg);color:var(--ink)}
a{color:var(--brand);text-decoration:none}
a:hover{text-decoration:underline}

/* Top bar */
.topbar{display:flex;align-items:center;gap:20px;background:var(--card);border-bottom:1px solid var(--line);padding:12px 20px;position:sticky;top:0;z-index:20}
.nav-toggle{display:none;background:transparent;border:1px solid var(--line);border-radius:8px;font-size:20px;line-height:1;padding:6px 10px;cursor:pointer;color:var(--ink)}
.thread-back{display:none;background:transparent;border:0;font-size:22px;line-height:1;margin-right:8px;cursor:pointer;color:var(--ink)}
.btn-primary,button.btn-primary,.btn-ghost,.btn-danger,.oauth-btn{min-height:44px}
img,video{max-width:100%}
.tabbar{display:none}
.mainnav .nav-secondary{display:none}
.brand{font-weight:800;font-size:20px;color:var(--brand)}
.brand:hover{text-decoration:none}
.mainnav{display:flex;gap:18px}
.mainnav a{color:var(--ink);font-weight:600}
.topbar-right{margin-left:auto;display:flex;align-items:center;gap:14px}
.lang-switch{border:1px solid var(--line);border-radius:999px;padding:4px 12px;color:var(--muted);font-size:13px}
.hello{color:var(--muted);margin-right:6px}

.container{max-width:1080px;margin:24px auto;padding:0 16px}

/* Buttons + forms */
.btn-primary,button.btn-primary{background:var(--brand);color:#fff;border:0;border-radius:8px;padding:9px 16px;font-weight:600;cursor:pointer}
.btn-primary:hover{background:var(--brand-dark);text-decoration:none}
.btn-link{color:var(--ink);font-weight:600}
.btn-ghost{background:transparent;border:1px solid var(--line);border-radius:8px;padding:8px 14px;cursor:pointer}
.btn-danger{background:var(--err);color:#fff;border:0;border-radius:8px;padding:8px 14px;cursor:pointer}
label{display:block;font-size:13px;color:var(--muted);margin:10px 0 4px}
input,select,textarea{width:100%;padding:10px 12px;border:1px solid var(--line);border-radius:8px;font-size:16px;font-family:inherit;background:#fff}
textarea{min-height:120px;resize:vertical}
.form-card{max-width:440px;margin:0 auto;background:var(--card);border:1px solid var(--line);border-radius:var(--radius);padding:28px}
.form-card h1{margin:0 0 4px;font-size:24px}
.form-card .sub{color:var(--muted);margin:0 0 18px}
.form-actions{margin-top:18px}
.row{display:flex;gap:12px}
.row>*{flex:1}
.divider{display:flex;align-items:center;text-align:center;color:var(--muted);font-size:13px;margin:18px 0}
.divider::before,.divider::after{content:"";flex:1;border-top:1px solid var(--line)}
.divider:not(:empty)::before{margin-right:10px}
.divider:not(:empty)::after{margin-left:10px}
.oauth-row{display:flex;gap:10px}
.oauth-btn{flex:1;border:1px solid var(--line);border-radius:8px;padding:9px;text-align:center;background:#fff;cursor:pointer;font-weight:600}
.switch-line{margin-top:16px;text-align:center;color:var(--muted);font-size:14px}

/* Search / toolbar */
.toolbar{display:flex;gap:10px;flex-wrap:wrap;align-items:end;background:var(--card);border:1px solid var(--line);border-radius:var(--radius);padding:14px;margin-bottom:20px}
.toolbar .grow{flex:1;min-width:200px}
.toolbar label{margin:0 0 4px}

/* Item grid */
.grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(210px,1fr));gap:16px}
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);overflow:hidden;transition:box-shadow .15s;cursor:pointer}
.card:hover{box-shadow:0 6px 18px rgba(0,0,0,.08)}
.card .thumb{width:100%;aspect-ratio:1/1;object-fit:cover;background:#eef1f4;display:block}
.card .body{padding:10px 12px}
.card .price{font-weight:800;font-size:17px}
.card .title{font-size:14px;margin:2px 0;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}
.card .meta{color:var(--muted);font-size:12px}
.badge{display:inline-block;background:#eef2ff;color:var(--brand);border-radius:999px;padding:2px 8px;font-size:11px;margin-left:6px}
.badge.sold{background:#fee2e2;color:var(--err)}

.section-title{font-size:15px;color:var(--muted);margin:22px 0 10px;font-weight:700;text-transform:uppercase;letter-spacing:.04em}
.empty{color:var(--muted);text-align:center;padding:40px}

/* Item detail */
.detail{display:grid;grid-template-columns:1.1fr .9fr;gap:24px}
.gallery .main-img{width:100%;border-radius:var(--radius);aspect-ratio:4/3;object-fit:cover;background:#eef1f4}
.thumbs{display:flex;gap:8px;margin-top:8px;flex-wrap:wrap}
.thumbs img{width:64px;height:64px;object-fit:cover;border-radius:8px;cursor:pointer;border:2px solid transparent}
.thumbs img.active{border-color:var(--brand)}
.detail h1{margin:0 0 6px}
.detail .price{font-size:26px;font-weight:800}

/* Conversations */
.conv-layout{display:grid;grid-template-columns:320px 1fr;gap:0;background:var(--card);border:1px solid var(--line);border-radius:var(--radius);overflow:hidden;min-height:70vh}
.conv-list{border-right:1px solid var(--line);overflow-y:auto}
.conv-item{display:flex;gap:10px;padding:12px;border-bottom:1px solid var(--line);cursor:pointer}
.conv-item:hover,.conv-item.active{background:#f0f5ff}
.conv-item img{width:44px;height:44px;border-radius:8px;object-fit:cover;background:#eef1f4}
.conv-item .ct{flex:1;min-width:0}
.conv-item .ct .nm{font-weight:600;font-size:14px}
.conv-item .ct .lm{color:var(--muted);font-size:13px;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.unread-dot{width:9px;height:9px;border-radius:50%;background:var(--brand);align-self:center}
.thread{display:flex;flex-direction:column}
.thread-head{padding:12px 16px;border-bottom:1px solid var(--line);font-weight:700}
.messages{flex:1;overflow-y:auto;padding:16px;display:flex;flex-direction:column;gap:8px}
.msg{max-width:70%;padding:9px 13px;border-radius:14px;font-size:14px;line-height:1.4}
.msg.them{background:#eef1f4;align-self:flex-start;border-bottom-left-radius:4px}
.msg.me{background:var(--brand);color:#fff;align-self:flex-end;border-bottom-right-radius:4px}
.msg.note{align-self:center;background:#fff7ed;color:#9a3412;font-size:12px;border:1px solid #fed7aa}
.composer{display:flex;gap:8px;padding:12px;border-top:1px solid var(--line)}
.composer input{flex:1}

/* Image upload previews */
.uploads{display:flex;gap:8px;flex-wrap:wrap;margin-top:8px}
.uploads .up{position:relative;width:80px;height:80px}
.uploads img{width:80px;height:80px;object-fit:cover;border-radius:8px}
.uploads .main-tag{position:absolute;top:2px;left:2px;background:var(--brand);color:#fff;font-size:10px;padding:1px 5px;border-radius:5px}
.uploads .x{position:absolute;top:-6px;right:-6px;background:var(--err);color:#fff;border:0;border-radius:50%;width:20px;height:20px;cursor:pointer}

/* Toast */
.toast{position:fixed;bottom:24px;left:50%;transform:translateX(-50%);color:#fff;padding:11px 18px;border-radius:8px;z-index:100;box-shadow:0 6px 20px rgba(0,0,0,.2)}
.toast.ok{background:var(--ok)}
.toast.err{background:var(--err)}

/* ---------------- Responsive / mobile ---------------- */
@media(max-width:760px){
  .container{margin:14px auto;padding:0 12px}

  /* Top bar collapses to brand + controls, with a hamburger for nav links */
  .topbar{flex-wrap:wrap;gap:10px 14px;padding:10px 14px}
  .brand{flex:1;font-size:18px}
  body.nav-hamburger .nav-toggle{display:flex;order:3}
  .topbar-right{order:2;margin-left:0;gap:10px}
  .mainnav{display:none;order:10;flex-basis:100%;flex-direction:column;gap:0}
  .topbar.open .mainnav{display:flex}
  .mainnav a{padding:12px 4px;border-top:1px solid var(--line)}
  body.nav-hamburger .topbar-right{display:none}
  .mainnav .nav-secondary{display:flex;flex-direction:column;gap:0}
  .mainnav .nav-secondary .hello{padding:12px 4px 4px;border-top:1px solid var(--line)}
  body.nav-tabbar .mainnav .nav-primary{display:none}

  /* Listings: two compact columns */
  .grid{grid-template-columns:repeat(2,1fr);gap:10px}
  .card .price{font-size:15px}
  .card .title{font-size:13px}
  .section-title{margin:16px 0 8px}

  /* Search toolbar stacks; each control full width */
  .toolbar{padding:10px;gap:8px}
  .toolbar .grow,.toolbar>div,.toolbar input,.toolbar select,.toolbar button{min-width:100%;max-width:100%}
  .toolbar button{width:100%}

  /* Item detail single column */
  .detail{grid-template-columns:1fr;gap:16px}
  .detail h1{font-size:20px}
  .detail .price{font-size:22px}

  /* Forms comfortably full-width */
  .form-card{max-width:100%;padding:20px 16px}
  .row{flex-direction:column;gap:0}

  /* Conversations: one pane at a time, with a back button */
  .conv-layout{grid-template-columns:1fr;min-height:auto}
  .conv-list{border-right:0;max-height:none}
  .thread{display:none;min-height:60vh}
  .conv-layout.show-thread .conv-list{display:none}
  .conv-layout.show-thread .thread{display:flex}
  .thread-back{display:inline-block}
  .messages{max-height:none}
  .msg{max-width:85%}

  /* Bottom tab bar (phones) — enabled via body.nav-tabbar */
  body.nav-tabbar{padding-bottom:64px}
  body.nav-tabbar .tabbar{display:flex;position:fixed;left:0;right:0;bottom:0;z-index:30;
    background:var(--card);border-top:1px solid var(--line)}
  .tabbar a{flex:1;display:flex;flex-direction:column;align-items:center;gap:2px;
    padding:8px 0 9px;font-size:11px;color:var(--muted);text-decoration:none}
  .tabbar a.active{color:var(--brand)}
  .tabbar a:hover{text-decoration:none}
  .tabbar svg{width:22px;height:22px}
}

/* Small phones */
@media(max-width:380px){
  .grid{grid-template-columns:1fr}
}