/* ── Apple Design System v3 ── */
:root {
  /* iOS 18 color tokens */
  --bg: #F2F2F7;
  --bg-elevated: #FFFFFF;
  --card: rgba(255,255,255,0.78);
  --card-solid: #FFFFFF;
  --text: #000000;
  --text2: rgba(60,60,67,0.6);
  --text3: rgba(60,60,67,0.3);
  --sep: rgba(60,60,67,0.08);
  --sep2: rgba(60,60,67,0.14);
  --fill: rgba(120,120,128,0.16);
  --fill2: rgba(120,120,128,0.1);
  --fill3: rgba(120,120,128,0.06);

  --blue: #007AFF;
  --green: #34C759;
  --orange: #FF9500;
  --red: #FF3B30;
  --purple: #AF52DE;
  --teal: #5AC8FA;
  --indigo: #5856D6;
  --pink: #FF2D55;
  --yellow: #FFCC00;
  --mint: #00C7BE;

  --accent: #5B6E82;
  --accent-light: #8FA3B5;
  --accent-bg: rgba(91,110,130,0.1);
  --accent-bg2: rgba(91,110,130,0.16);

  --r-xs: 8px; --r-sm: 12px; --r: 16px; --r-lg: 20px; --r-xl: 24px;

  --sh-sm: 0 1px 3px rgba(0,0,0,0.04);
  --sh: 0 2px 12px rgba(0,0,0,0.06);
  --sh-lg: 0 8px 32px rgba(0,0,0,0.08);

  --ease: cubic-bezier(0.25, 0.1, 0.25, 1);
  --spring: cubic-bezier(0.22, 0.61, 0.36, 1);
  --bounce: cubic-bezier(0.34, 1.56, 0.64, 1);
  --snap: cubic-bezier(0.16, 1, 0.3, 1);

  --font: -apple-system, BlinkMacSystemFont, "SF Pro Display", "SF Pro Text", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif;
  --safe: env(safe-area-inset-bottom, 16px);

  /* Legacy aliases */
  --c1: var(--accent); --c2: var(--accent-light);
  --c3: var(--accent-bg); --c4: #1C1C1E;
  --bdr: var(--sep);
}

*,*::before,*::after{margin:0;padding:0;box-sizing:border-box;-webkit-tap-highlight-color:transparent}
html{-webkit-font-smoothing:antialiased;-moz-osx-font-smoothing:grayscale;scroll-behavior:smooth}
body{font-family:var(--font);background:var(--bg);color:var(--text);min-height:100dvh;letter-spacing:-0.01em;padding-bottom:100px;overflow-x:hidden}

/* ── Layout Container ── */
main{padding:12px 16px;max-width:720px;margin:0 auto}
@media(min-width:768px){main{padding:20px 24px}}

/* ── Header (sticky glass) ── */
.header{
  position:sticky;top:0;z-index:50;
  background:rgba(242,242,247,0.82);
  backdrop-filter:blur(24px) saturate(200%);
  -webkit-backdrop-filter:blur(24px) saturate(200%);
  padding:10px 20px;
  display:flex;align-items:center;gap:12px;
  border-bottom:0.33px solid var(--sep);
}
.header h1{font-size:20px;font-weight:700;letter-spacing:-0.02em;color:var(--text)}
.header .back{width:34px;height:34px;background:var(--fill3);border:none;border-radius:50%;display:flex;align-items:center;justify-content:center;font-size:17px;color:var(--accent);cursor:pointer;text-decoration:none;transition:all 0.15s}
.header .back:active{background:var(--fill2);transform:scale(0.86)}

@media(min-width:768px){
  .header{padding:12px 28px;border-radius:0}
  .header h1{font-size:24px}
}

/* ── Bottom Navigation Bar ── */
.nav-bar{
  position:fixed;bottom:0;left:0;right:0;
  background:rgba(255,255,255,0.85);
  backdrop-filter:blur(24px) saturate(180%);
  -webkit-backdrop-filter:blur(24px) saturate(180%);
  display:flex;justify-content:space-around;
  padding:6px 0 max(6px,var(--safe));
  border-top:0.5px solid var(--sep);
  z-index:100;
}
.nav-item{
  display:flex;flex-direction:column;align-items:center;gap:2px;
  text-decoration:none;color:var(--text2);
  font-size:10px;font-weight:500;cursor:pointer;
  transition:color 0.2s;
  -webkit-tap-highlight-color:transparent;
}
.nav-item .ni{font-size:22px}
.nav-item.active{color:var(--accent);font-weight:600}
@media(min-width:768px){
  .nav-bar{justify-content:center;gap:32px}
  .nav-item{flex-direction:row;gap:6px;font-size:13px;padding:10px 16px}
  .nav-item .ni{font-size:20px}
}

/* ── Card ── */
.card{
  background:var(--card);
  backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);
  border-radius:var(--r);padding:20px;margin-bottom:12px;
  box-shadow:var(--sh-sm);border:0.33px solid rgba(0,0,0,0.04);
  transition:transform 0.2s var(--spring),box-shadow 0.2s var(--spring);
}
.card:active{transform:scale(0.985)}
@media(min-width:768px){.card{padding:24px}}

/* ── Buttons ── */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:6px;
  padding:12px 22px;border:none;border-radius:var(--r-sm);
  font-size:15px;font-weight:600;font-family:var(--font);
  cursor:pointer;letter-spacing:-0.01em;
  transition:all 0.2s var(--spring);white-space:nowrap;
}
.btn:active{transform:scale(0.94)}
.btn-primary{background:var(--accent);color:white}
.btn-primary:active{opacity:0.85}
.btn-primary:disabled{opacity:0.35;pointer-events:none}
.btn-green{background:var(--green);color:white}
.btn-red{background:var(--red);color:white}
.btn-blue{background:var(--blue);color:white}
.btn-purple{background:var(--purple);color:white}
.btn-outline{background:var(--fill3);color:var(--text);border:0.5px solid var(--sep2)}
.btn-sm{padding:7px 14px;font-size:13px;border-radius:10px;width:auto}
.btn-icon{width:36px;height:36px;padding:0;border-radius:50%;font-size:16px}

/* ── Inputs ── */
input,textarea,select{
  font-family:var(--font);font-size:15px;
  border:0.5px solid var(--sep2);border-radius:var(--r-sm);
  padding:12px 16px;background:var(--card-solid);color:var(--text);
  width:100%;outline:none;
  transition:all 0.2s var(--ease);-webkit-appearance:none;
}
input:focus,textarea:focus,select:focus{
  border-color:var(--accent);box-shadow:0 0 0 4px var(--accent-bg);
}
textarea{min-height:80px;line-height:1.5;resize:vertical}
select{
  background-image:url("data:image/svg+xml,%3Csvg width='12' height='8' viewBox='0 0 12 8'%3E%3Cpath d='M1 1l5 5 5-5' stroke='%23888' stroke-width='1.5' fill='none'/%3E%3C/svg%3E");
  background-repeat:no-repeat;background-position:right 14px center;padding-right:38px;
}

/* ── Modal (iOS Sheet) ── */
.modal-overlay{
  display:none;position:fixed;inset:0;background:rgba(0,0,0,0.35);
  z-index:200;align-items:flex-end;justify-content:center;
}
.modal-overlay.show{display:flex}
.modal{
  background:var(--card-solid);border-radius:var(--r-lg) var(--r-lg) 0 0;
  padding:28px 24px;width:100%;max-width:560px;max-height:85dvh;
  overflow-y:auto;box-shadow:0 -8px 48px rgba(0,0,0,0.12);
  animation:sheetUp 0.38s var(--spring);
}
@keyframes sheetUp{from{transform:translateY(100%)}to{transform:translateY(0)}}
.modal h3{font-size:18px;font-weight:700;margin-bottom:16px}
.modal label{display:block;font-size:12px;font-weight:600;color:var(--text2);margin:12px 0 4px;text-transform:uppercase;letter-spacing:0.04em}

/* ── Stats ── */
.stats-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(80px,1fr));gap:8px}
.stat-box{background:var(--fill3);border-radius:var(--r-sm);padding:16px 12px;text-align:center;transition:transform 0.2s var(--spring)}
.stat-box:active{transform:scale(0.93)}
.stat-box .val{font-size:24px;font-weight:700;letter-spacing:-0.03em}
.stat-box .lbl{font-size:11px;color:var(--text2);margin-top:2px}
@media(min-width:768px){.stat-box .val{font-size:28px}}

/* ── Filter Tags ── */
.filter-bar{display:flex;gap:4px;padding:4px;background:var(--fill3);border-radius:var(--r-sm);margin-bottom:12px}
.filter-tag{flex:1;text-align:center;padding:7px 12px;border-radius:10px;font-size:13px;font-weight:500;background:transparent;color:var(--text2);border:none;cursor:pointer;transition:all 0.2s var(--spring)}
.filter-tag.active{background:var(--card-solid);color:var(--text);font-weight:600;box-shadow:var(--sh-sm)}
.filter-tag:active{transform:scale(0.94)}

/* ── Tabs ── */
.tab-bar{display:flex;gap:2px;margin:12px 0;background:var(--fill3);border-radius:var(--r-sm);padding:3px}
.tab{flex:1;text-align:center;padding:9px 6px;border-radius:10px;font-size:13px;font-weight:500;cursor:pointer;color:var(--text2);transition:all 0.2s var(--spring)}
.tab.active{background:var(--card-solid);color:var(--text);font-weight:600;box-shadow:var(--sh-sm)}
.tab:active{transform:scale(0.94)}
.tab-content{display:none}.tab-content.active{display:block}

/* ── Badges ── */
.badge{font-size:11px;padding:4px 10px;border-radius:12px;font-weight:600;display:inline-block}
.badge-done{background:rgba(52,199,89,0.12);color:var(--green)}
.badge-pending{background:rgba(255,149,0,0.12);color:var(--orange)}
.badge-none{background:var(--fill3);color:var(--text2)}

/* ── Alerts ── */
.alert{padding:14px 18px;border-radius:var(--r-sm);font-size:13px;margin-bottom:12px;font-weight:500;line-height:1.5}
.alert-info{background:rgba(0,122,255,0.08);color:var(--blue)}
.alert-success{background:rgba(52,199,89,0.08);color:var(--green)}
.alert-error{background:rgba(255,59,48,0.08);color:var(--red)}

/* ── Empty State ── */
.empty-state{text-align:center;padding:64px 20px;color:var(--text2)}
.empty-state .ei{font-size:52px;margin-bottom:12px;opacity:0.5}

/* ── Spinner ── */
.spinner{width:18px;height:18px;border:2.5px solid var(--fill);border-top-color:var(--accent);border-radius:50%;animation:spin 0.75s linear infinite;display:inline-block;vertical-align:middle;margin-right:6px}
@keyframes spin{to{transform:rotate(360deg)}}

/* ── Student / HW cards ── */
.student-card,.hw-item{
  background:var(--card);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);
  border-radius:var(--r);padding:14px 16px;margin-bottom:8px;
  border:0.33px solid rgba(0,0,0,0.04);box-shadow:var(--sh-sm);
  cursor:pointer;transition:all 0.2s var(--spring);
}
.student-card:active,.hw-item:active{transform:scale(0.985);background:var(--fill3)}

/* ── Upload Area ── */
.upload-area{
  background:var(--fill3);border:1.5px dashed var(--sep2);
  border-radius:var(--r-sm);padding:28px;text-align:center;
  cursor:pointer;transition:all 0.2s var(--ease);
}
.upload-area:active{border-color:var(--accent);background:var(--accent-bg);transform:scale(0.98)}

/* ── Image Previews ── */
.st-imgs,.upload-preview{display:flex;flex-wrap:wrap;gap:6px;margin-top:10px}
.st-imgs img,.upload-preview img{width:72px;height:72px;object-fit:cover;border-radius:var(--r-xs);border:0.5px solid var(--sep);transition:transform 0.2s}
.st-imgs img:active,.upload-preview img:active{transform:scale(2.2);z-index:10;box-shadow:var(--sh-lg)}

/* ── Table ── */
.table-wrap{overflow-x:auto;-webkit-overflow-scrolling:touch}
table{width:100%;border-collapse:collapse;font-size:13px}
th{background:var(--fill3);padding:10px 8px;text-align:left;font-size:11px;font-weight:600;color:var(--text2);text-transform:uppercase;letter-spacing:0.04em;border-bottom:0.5px solid var(--sep)}
td{padding:10px 8px;border-bottom:0.5px solid var(--sep)}
tr:active td{background:var(--fill3)}
@media(min-width:768px){th,td{padding:12px 14px}}

/* ── Trend Chart ── */
.trend-chart{display:flex;align-items:flex-end;gap:3px;padding:12px 10px;height:160px;background:var(--fill3);border-radius:var(--r-sm);overflow-x:auto}
.trend-bar{flex-shrink:0;width:22px;border-radius:5px 5px 0 0;min-height:4px;transition:height 0.4s var(--spring);position:relative;cursor:pointer}
.trend-bar .tip{position:absolute;bottom:102%;left:50%;transform:translateX(-50%);font-size:9px;white-space:nowrap;color:var(--text2);opacity:0;transition:opacity 0.2s}
.trend-bar:hover .tip{opacity:1}

/* ── Slot Grid (批改通道) ── */
.slots-grid{display:flex;flex-direction:column;gap:12px}
.slot{background:var(--card);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);border-radius:var(--r);padding:16px;border:2px solid var(--sep);transition:all 0.3s var(--spring);position:relative}
.slot.ready{border-color:var(--accent);box-shadow:0 0 0 2px var(--accent-bg)}
.slot.correcting{border-color:var(--blue);animation:pulse 1.2s infinite}
.slot.done-good{border-color:var(--green);background:rgba(52,199,89,0.04)}
.slot.done-weak{border-color:var(--orange);background:rgba(255,149,0,0.04)}
@keyframes pulse{0%,100%{opacity:1}50%{opacity:0.6}}
.slot select{width:100%;margin-top:8px}
.slot-upload{width:100%;aspect-ratio:16/10;background:var(--fill3);border:1.5px dashed var(--sep2);border-radius:var(--r-sm);display:flex;flex-direction:column;align-items:center;justify-content:center;cursor:pointer;margin-top:8px;position:relative;overflow:hidden;transition:all 0.2s}
.slot-upload.has-img{border-style:solid;border-color:var(--accent)}
.slot-upload img{position:absolute;inset:0;width:100%;height:100%;object-fit:contain;border-radius:var(--r-xs)}
.slot-upload .img-tag{position:absolute;bottom:6px;right:6px;background:rgba(0,0,0,0.6);color:white;font-size:10px;padding:2px 8px;border-radius:8px}
@media(min-width:768px){.slots-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:12px}}

/* ── Quick Actions Grid ── */
.quick-actions{display:grid;grid-template-columns:1fr 1fr;gap:10px;margin-bottom:16px}
.quick-card{background:var(--card);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);border-radius:var(--r);padding:20px 16px;border:0.33px solid rgba(0,0,0,0.04);cursor:pointer;transition:all 0.2s var(--spring);text-decoration:none;color:var(--text);box-shadow:var(--sh-sm);display:flex;flex-direction:column;gap:6px}
.quick-card:active{transform:scale(0.95)}
.quick-card .icon{font-size:30px}
.quick-card .label{font-size:15px;font-weight:600}
.quick-card .sub{font-size:12px;color:var(--text2)}
@media(min-width:768px){.quick-actions{grid-template-columns:repeat(4,1fr)}}

/* ── Forms ── */
.form-row{display:flex;gap:10px;flex-wrap:wrap}
.form-row>*{flex:1;min-width:120px}
.form-label{font-size:12px;font-weight:600;color:var(--text2);margin-bottom:5px;display:block}

/* ── Answer Bar ── */
.answer-bar{background:var(--card);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);border-radius:var(--r);padding:12px 16px;margin-bottom:12px;box-shadow:var(--sh-sm);border:0.33px solid rgba(0,0,0,0.04);display:flex;align-items:center;gap:12px;flex-wrap:wrap}

/* ── Question Table ── */
.q-table{background:var(--card);border-radius:var(--r);overflow:hidden;border:0.33px solid rgba(0,0,0,0.04);margin-bottom:12px}
.q-row{display:flex;align-items:center;padding:12px 14px;border-bottom:0.5px solid var(--sep)}
.q-row:last-child{border-bottom:none}
.q-row.header{background:var(--fill3);font-weight:700;font-size:12px;color:var(--accent);text-transform:uppercase;letter-spacing:0.03em}
.q-cell{flex:1;padding:0 6px;font-size:13px}
.q-cell input,.q-cell select{padding:8px 10px;font-size:13px;background:var(--fill3)}
.q-cell.del{cursor:pointer;color:var(--red);font-size:16px;text-align:center;flex:0 0 30px}

/* ── HW Detail ── */
.hw-detail{display:none;margin-top:10px;padding-top:10px;border-top:0.5px solid var(--sep)}
.hw-detail.show{display:block}

/* ── Hero ── */
.hero{text-align:center;padding:36px 20px 28px}
.hero h1{font-size:30px;font-weight:800;letter-spacing:-0.03em;margin-bottom:4px;color:var(--accent)}
.hero p{font-size:16px;color:var(--text2)}
@media(min-width:768px){.hero{padding:52px 20px 36px}.hero h1{font-size:38px}.hero p{font-size:18px}}

/* ── Realtime Progress ── */
.progress-bar{background:var(--fill3);border-radius:20px;height:8px;overflow:hidden;margin:12px 0}
.progress-fill{background:var(--accent);height:100%;border-radius:20px;transition:width 0.5s var(--spring);min-width:2px}

/* ── Zoom overlay ── */
.img-zoom-overlay{display:none;position:fixed;inset:0;background:rgba(0,0,0,0.9);z-index:300;align-items:center;justify-content:center}
.img-zoom-overlay.show{display:flex}
.img-zoom-overlay img{max-width:95vw;max-height:95vh;object-fit:contain;border-radius:4px}

/* ── Reduced Motion ── */
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation-duration:0.01ms!important;transition-duration:0.01ms!important}}

/* ── Dark Mode ── */
@media(prefers-color-scheme:dark){
  :root{
    --bg:#000000;--bg-elevated:#1C1C1E;--card:rgba(28,28,30,0.82);--card-solid:#1C1C1E;
    --text:#FFFFFF;--text2:rgba(235,235,245,0.6);--text3:rgba(235,235,245,0.3);
    --sep:rgba(84,84,88,0.65);--sep2:rgba(84,84,88,0.8);
    --fill:rgba(120,120,128,0.36);--fill2:rgba(120,120,128,0.24);--fill3:rgba(120,120,128,0.14);
    --accent:#8FA3B5;--accent-light:#A8B9C8;
    --accent-bg:rgba(143,163,181,0.14);--accent-bg2:rgba(143,163,181,0.22);
    --sh-sm:0 1px 3px rgba(0,0,0,0.4);--sh:0 2px 12px rgba(0,0,0,0.5);--sh-lg:0 8px 32px rgba(0,0,0,0.6);
  }
  .nav-bar{background:rgba(28,28,30,0.85)}
  .header{background:rgba(0,0,0,0.85);border-bottom-color:var(--sep)}
  .modal{background:rgba(28,28,30,0.98)}
  input,textarea,select{background:rgba(255,255,255,0.06);color:var(--text)}
  input:focus,textarea:focus,select:focus{background:rgba(255,255,255,0.1)}
  .filter-bar{background:var(--fill3)}
  .filter-tag.active{background:var(--fill)}
  .tab-bar{background:var(--fill3)}
  .tab.active{background:var(--fill)}
  .student-card,.hw-item{background:var(--card)}
  .slot-upload{background:var(--fill3)}
}