/* Faktorisasi Aljabar: gaya bersama untuk tiga laman (pengantar, animasi, latihan).
   Token warna Warm Nordic v4.1 (UI_WARM_NORDIC_REFACTOR_PROMPT.md), ditambah token kontras yang dicatat di laporan. */

:root,
[data-theme="light"] {
  --bg-canvas: #F8F5EE;
  --bg-surface: #FFFFFF;
  --bg-subtle: #EFE9DC;
  --bg-hover: #E7E0D0;
  --bg-card-warm: #FDFBF7;

  --ink-primary: #1C201D;
  --ink-secondary: #47504A;

  --border-subtle: #E4DCCF;
  --border-strong: #C9BEAC;
  /* Batas kontrol (input, tombol sekunder) butuh 3:1. --border-strong hanya 1.69:1, jadi dipakai --scale-beam. */
  --line-ui: #8C7B65;

  --brand: #235340;
  --brand-hover: #1A3E30;
  --brand-active: #133025;
  --brand-soft: #E5EFEA;
  --brand-text: #194031;
  --on-primary: #FFFFFF;

  /* Putih di atas --accent (#C86D24) hanya 3.70:1, jadi isi tombol aksen memakai --accent-hover. */
  --accent-btn: #A75718;
  --accent-btn-hover: #8A4611;
  --accent-btn-edge: #6E3608;
  --on-accent-btn: #FFFFFF;
  --accent-soft: #FBF0E4;
  --accent-border: #ECCAA8;
  --accent-text: #8E4410;

  --success-soft: #E6F3EB;
  --success-border: #A3D4B8;
  --success-text: #1E4F36;
  --info-soft: #EAF1F5;
  --info-border: #A9C8D9;
  --info-text: #214152;
  --danger-soft: #FAEBEA;
  --danger-border: #E8AFA9;
  --danger-text: #7D2820;

  --tile-num-bg: #EAE3D2;
  --tile-num-border: #C8BA9E;
  --tile-num-ink: #2C281F;
  --tile-var-bg: #D1E5DA;
  --tile-var-border: #99C3AD;
  --tile-var-ink: #143A28;
  --tile-common-bg: #FBF0E4;
  --tile-common-border: #A75718;
  --tile-common-ink: #8E4410;

  --focus: #235340;
  --shadow-tactile-sm: 0 2px 0 var(--border-strong);
  --shadow-tactile-primary: 0 3px 0 #133025;
}

[data-theme="dark"] {
  --bg-canvas: #121715;
  --bg-surface: #19201C;
  --bg-subtle: #212B26;
  --bg-hover: #2B3731;
  --bg-card-warm: #1D2521;

  --ink-primary: #EDE8DF;
  --ink-secondary: #AFBDB4;

  --border-subtle: #2A3630;
  --border-strong: #3B4A42;
  --line-ui: #687970;

  --brand: #459E7A;
  --brand-hover: #58B690;
  --brand-active: #348061;
  --brand-soft: rgba(69, 158, 122, 0.16);
  --brand-text: #8DD4B5;
  /* Teks terang di atas #459E7A hanya 2.68:1, jadi tombol primer gelap memakai teks gelap. */
  --on-primary: #121715;

  --accent-btn: #E08234;
  --accent-btn-hover: #EE964D;
  --accent-btn-edge: #6B3B15;
  --on-accent-btn: #121715;
  --accent-soft: rgba(224, 130, 52, 0.16);
  --accent-border: #6B3B15;
  --accent-text: #F7BA83;

  --success-soft: rgba(69, 158, 122, 0.16);
  --success-border: #265942;
  --success-text: #8DD4B5;
  --info-soft: rgba(86, 145, 175, 0.16);
  --info-border: #234859;
  --info-text: #96C5DE;
  --danger-soft: rgba(223, 93, 82, 0.16);
  --danger-border: #6B2620;
  --danger-text: #F4A199;

  --tile-num-bg: #2C2920;
  --tile-num-border: #4D4636;
  --tile-num-ink: #EDE8DF;
  --tile-var-bg: #1B3125;
  --tile-var-border: #2D5841;
  --tile-var-ink: #D1E5DA;
  --tile-common-bg: #3A2A1C;
  --tile-common-border: #E08234;
  --tile-common-ink: #F7BA83;

  --focus: #8DD4B5;
  --shadow-tactile-sm: 0 2px 0 var(--border-strong);
  --shadow-tactile-primary: 0 3px 0 #1E4F3B;
}

:root {
  --radius-sm: 6px;
  --radius-md: 10px;
  --radius-lg: 14px;
  --font-body: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  /* Satu keluarga untuk semua angka dan huruf matematika: STIX Two Text (dimuat dengan display=optional,
     jadi font tidak pernah berganti setelah laman tampil). Cadangan hanya dipakai bila font belum siap saat laman dibuka. */
  --font-math: "STIX Two Text", "STIX Two Math", Cambria, Georgia, "Times New Roman", serif;
  --ease-tactile: cubic-bezier(0.2, 0.8, 0.2, 1);
  --t-fast: 140ms;
}

*, *::before, *::after { box-sizing: border-box; }
[hidden] { display: none !important; }
html { -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  background: var(--bg-canvas);
  color: var(--ink-primary);
  font-family: var(--font-body);
  font-size: 1rem;
  line-height: 1.55;
}
h1, h2, h3 { line-height: 1.2; margin: 0; }
p { margin: 0; }
button, input { font: inherit; color: inherit; }
a { color: var(--brand-text); text-underline-offset: 3px; }
:focus-visible { outline: 3px solid var(--focus); outline-offset: 2px; }

.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0;
}
.skip {
  position: absolute; left: 16px; top: -60px;
  background: var(--bg-surface); color: var(--ink-primary);
  padding: 10px 14px; border: 2px solid var(--focus); border-radius: var(--radius-md);
  z-index: 10;
}
.skip:focus { top: 12px; }

.wrap { max-width: 1040px; margin: 0 auto; padding: 0 16px 56px; }

/* ---------- Kepala laman dan navigasi antarlaman ---------- */
.site-head {
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between;
  gap: 8px 16px;
  padding: 18px 0 12px;
}
.site-name {
  font-weight: 800; font-size: 1.05rem; color: var(--ink-primary); text-decoration: none;
  display: inline-flex; align-items: center; min-height: 44px;
}
.site-name:hover { text-decoration: underline; }

/* Tiga laman berurutan. Nomor menunjukkan urutan belajar, aria-current menandai laman yang sedang dibuka. */
.pages {
  display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 6px;
  margin: 0 0 28px; padding: 6px;
  background: var(--bg-subtle);
  border-radius: var(--radius-lg);
}
.pages a {
  display: flex; align-items: center; justify-content: center; gap: 6px;
  min-height: 48px; padding: 6px 8px;
  border-radius: var(--radius-md);
  color: var(--ink-primary); font-weight: 600; text-decoration: none; text-align: center;
  line-height: 1.2;
}
.pages a .num {
  display: inline-flex; align-items: center; justify-content: center;
  width: 1.6em; height: 1.6em; border-radius: 50%;
  border: 1px solid var(--line-ui); font-size: 0.85rem;
  flex: none;
}
.pages a:hover { background: var(--bg-hover); }
.pages a[aria-current="page"] {
  background: var(--bg-surface);
  color: var(--brand-text);
  box-shadow: inset 0 0 0 2px var(--brand);
}
.pages a[aria-current="page"] .num { background: var(--brand); border-color: var(--brand); color: var(--on-primary); }
@media (max-width: 400px) {
  .pages a { flex-direction: column; gap: 2px; font-size: 0.9rem; }
}

.page-head { margin-bottom: 20px; max-width: 62ch; }
.page-head h1 { font-size: clamp(1.6rem, 1.2rem + 1.8vw, 2.3rem); font-weight: 800; letter-spacing: -0.01em; }
.page-head p { margin-top: 8px; color: var(--ink-secondary); font-size: 1.05rem; }

.next-page {
  margin-top: 40px; padding-top: 20px;
  border-top: 1px solid var(--border-subtle);
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 12px;
}
.next-page p { color: var(--ink-secondary); }

/* ---------- Tombol ---------- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  font-weight: 600; font-size: 0.95rem;
  padding: 10px 18px; min-height: 44px;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  user-select: none;
  text-decoration: none;
  transition: transform var(--t-fast) var(--ease-tactile),
              box-shadow var(--t-fast) var(--ease-tactile),
              background-color var(--t-fast) ease;
}
.btn:disabled { cursor: not-allowed; opacity: 0.55; }
.btn--primary {
  background: var(--brand); color: var(--on-primary);
  border-color: var(--brand-active);
  box-shadow: var(--shadow-tactile-primary);
}
.btn--primary:hover:not(:disabled) { background: var(--brand-hover); transform: translateY(-1px); }
.btn--primary:active:not(:disabled) { transform: translateY(2px); box-shadow: 0 1px 0 var(--brand-active); }
.btn--accent {
  background: var(--accent-btn); color: var(--on-accent-btn);
  border-color: var(--accent-btn-edge);
  box-shadow: 0 3px 0 var(--accent-btn-edge);
}
.btn--accent:hover:not(:disabled) { background: var(--accent-btn-hover); transform: translateY(-1px); }
.btn--accent:active:not(:disabled) { transform: translateY(2px); box-shadow: 0 1px 0 var(--accent-btn-edge); }
.btn--secondary {
  background: var(--bg-surface); color: var(--ink-primary);
  border-color: var(--line-ui);
  box-shadow: var(--shadow-tactile-sm);
}
.btn--secondary:hover:not(:disabled) { background: var(--bg-subtle); transform: translateY(-1px); }
.btn--secondary:active:not(:disabled) { transform: translateY(1px); box-shadow: 0 1px 0 var(--border-strong); }
.btn--secondary[aria-pressed="true"] {
  background: var(--brand-soft); border-color: var(--brand); color: var(--brand-text);
  box-shadow: inset 0 0 0 1px var(--brand);
}
.btn--ghost { background: transparent; color: var(--ink-secondary); border-color: transparent; }
.btn--ghost:hover:not(:disabled) { background: var(--bg-subtle); color: var(--ink-primary); }
.btn--theme { border-color: var(--line-ui); background: transparent; color: var(--ink-primary); }
.btn--theme:hover { background: var(--bg-subtle); }

.activity-box {
  background: var(--bg-card-warm);
  border: 1px solid var(--border-strong);
  border-radius: var(--radius-lg);
  padding: 20px;
}

/* ---------- Matematika: satu keluarga, satu ketebalan, di semua keadaan ---------- */
.math, .tile, .op, .paren, .dot, .term-card, .result-expr, .field, .vk-key--math, .choice label, .examples .btn {
  font-family: var(--font-math);
  font-weight: 400;
  font-variant-numeric: lining-nums;
  font-synthesis: none;
  letter-spacing: 0;
}
.math i, .tile--var, .term-card i, .result-expr i, .vk-key--var { font-style: italic; }
/* Pangkat ditulis dengan <sup> dari font yang sama, bukan karakter superskrip Unicode yang bisa diambil dari font lain. */
.math sup, .term-card sup, .result-expr sup, .problem-expr sup, .choice sup, .examples sup {
  font-size: 0.62em; line-height: 0; vertical-align: 0.62em; font-style: normal;
}
.caption .math, .feedback .math, .msg .math, .preview .math, p .math, li .math { font-size: 1.15em; }

/* ---------- Panggung animasi ---------- */
.examples-label, .speed legend { font-weight: 700; font-size: 0.95rem; margin-bottom: 8px; padding: 0; }
.examples { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 18px; }
.examples .btn { font-size: 1.15rem; }

.player-tools {
  display: flex; flex-wrap: wrap; justify-content: space-between; align-items: flex-end; gap: 12px 24px;
}

/* Pilihan kecepatan: segmen radio, default Lambat. */
.speed { border: 0; margin: 0 0 18px; padding: 0; min-width: 0; }
.seg { display: inline-flex; gap: 4px; padding: 4px; background: var(--bg-subtle); border-radius: var(--radius-md); }
.seg input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.seg label {
  display: inline-flex; align-items: center; min-height: 44px; padding: 6px 14px;
  border-radius: var(--radius-sm); cursor: pointer; font-weight: 600; color: var(--ink-secondary);
}
.seg label:hover { background: var(--bg-hover); color: var(--ink-primary); }
.seg input:checked + label { background: var(--bg-surface); color: var(--brand-text); box-shadow: inset 0 0 0 2px var(--brand); }
.seg input:focus-visible + label { outline: 3px solid var(--focus); outline-offset: 2px; }

.stage-head {
  display: flex; flex-wrap: wrap; justify-content: space-between; align-items: baseline;
  gap: 6px 16px; margin-bottom: 8px;
}
.step-count { font-weight: 700; color: var(--brand-text); }
.step-dots { display: flex; gap: 6px; }
.step-dots span { width: 22px; height: 6px; border-radius: 3px; background: var(--border-strong); }
.step-dots span.on { background: var(--brand); }

.stage {
  position: relative;
  background: var(--bg-surface);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-md);
  min-height: 220px;
  padding: 24px 12px;
  display: flex; align-items: center; justify-content: center;
  overflow: hidden;
}
.row {
  display: flex; flex-wrap: wrap; align-items: center; justify-content: center;
  gap: 14px 10px; max-width: 100%;
}
.group {
  display: inline-flex; flex-wrap: wrap; align-items: center; justify-content: center;
  gap: 6px 4px; padding: 8px;
  border: 1px dashed var(--border-strong);
  border-radius: var(--radius-md);
  max-width: 100%;
}
/* Tanda operasi selalu menempel ke suku sesudahnya saat baris membungkus di layar sempit. */
.unit { display: inline-flex; align-items: center; gap: 10px; max-width: 100%; }
.unit > .group { min-width: 0; }
.group--front { border: 2px solid var(--tile-common-border); background: var(--accent-soft); }
.group--plain { border-color: transparent; padding: 8px 2px; }

/* Semua teks di panggung memakai ukuran yang sama supaya bentuk angka dan huruf tidak melompat antarlangkah. */
.stage { --stage-size: 1.45rem; font-family: var(--font-math); font-weight: 400; font-synthesis: none; }
.op, .paren, .dot { font-size: var(--stage-size); color: var(--ink-primary); line-height: 1; }
.paren { font-size: calc(var(--stage-size) * 1.5); }
.dot { color: var(--ink-secondary); padding: 0 1px; }
.term-card {
  font-size: var(--stage-size);
  line-height: 1;
  padding: 12px 16px;
  border-radius: var(--radius-md);
  background: var(--bg-card-warm);
  border: 2px solid var(--line-ui);
  box-shadow: var(--shadow-tactile-sm);
}

/* Garis tepi selalu 2px, jadi menandai faktor bersama tidak menggeser tata letak. */
.tile {
  display: inline-flex; align-items: center; justify-content: center;
  min-width: 2.4rem; height: 2.6rem; padding: 0 8px;
  font-size: var(--stage-size);
  line-height: 1;
  border-radius: 8px;
  border: 2px solid;
  transition-property: background-color, border-color, color, box-shadow;
  transition-timing-function: ease;
  transition-duration: 0ms;
}
.tile--num { background: var(--tile-num-bg); border-color: var(--tile-num-border); color: var(--tile-num-ink); box-shadow: 0 2px 0 var(--tile-num-border); }
.tile--var { background: var(--tile-var-bg); border-color: var(--tile-var-border); color: var(--tile-var-ink); box-shadow: 0 2px 0 var(--tile-var-border); }
.tile--one { border-style: dashed; }
/* Faktor bersama ditandai warna dan garis tepi oranye, tanpa mengubah ketebalan atau bentuk huruf. */
.tile.is-common {
  background: var(--tile-common-bg);
  border-color: var(--tile-common-border);
  color: var(--tile-common-ink);
  box-shadow: 0 3px 0 var(--tile-common-border);
}
.tile.ghost { position: absolute; margin: 0; pointer-events: none; z-index: 2; }

.result { text-align: center; display: grid; gap: 16px; justify-items: center; }
.result-expr { font-size: calc(var(--stage-size) * 1.25); line-height: 1.3; }
.result-expr .front {
  color: var(--tile-common-ink);
  background: var(--tile-common-bg);
  border-bottom: 3px solid var(--tile-common-border);
  padding: 0 4px;
  border-radius: 4px 4px 0 0;
}
.result-check { font-size: 1.05rem; color: var(--ink-secondary); max-width: 36ch; }
.result-check .math { font-size: 1.2rem; color: var(--ink-primary); }

.caption { margin-top: 14px; min-height: 3.2em; font-size: 1.05rem; max-width: 66ch; }
.caption .lines { display: block; margin-top: 6px; }
.caption .lines span { display: block; }

.controls { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 16px; align-items: center; }
.controls .spacer { flex: 1 1 0; }

.from-practice {
  margin-bottom: 16px; padding: 12px 14px;
  border-radius: var(--radius-md);
  background: var(--info-soft); border: 1px solid var(--info-border); color: var(--info-text);
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between; gap: 8px 16px;
}
.from-practice a { color: var(--info-text); font-weight: 700; min-height: 44px; display: inline-flex; align-items: center; }

.custom { margin-top: 24px; padding-top: 20px; border-top: 1px solid var(--border-subtle); }
.custom > label { display: block; font-weight: 700; }
.custom .hint { color: var(--ink-secondary); font-size: 0.95rem; margin: 2px 0 10px; }
.custom-row { display: flex; flex-wrap: wrap; gap: 10px; }
.custom-row .field { flex: 1 1 220px; min-width: 0; }

.field {
  min-height: 52px;
  padding: 8px 12px;
  border: 2px solid var(--line-ui);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  color: var(--ink-primary);
  font-size: 1.35rem;
  width: 100%;
  min-width: 0;
}
.field[aria-invalid="true"] { border: 2px solid var(--danger-text); }
/* Kotak yang sedang menerima ketikan keyboard layar. */
.field.is-target { border-color: var(--brand); box-shadow: inset 0 0 0 1px var(--brand); }

.msg { margin-top: 10px; font-size: 0.98rem; }
.msg:empty { display: none; }
.msg--error { color: var(--danger-text); }
.msg--ok { color: var(--success-text); }

/* ---------- Keyboard layar ---------- */
.vk {
  margin-top: 14px;
  padding: 10px;
  background: var(--bg-subtle);
  border: 1px solid var(--border-subtle);
  border-radius: var(--radius-lg);
  max-width: 460px;
}
.vk-head {
  display: flex; flex-wrap: wrap; align-items: center; justify-content: space-between;
  gap: 4px 12px; margin-bottom: 8px;
}
.vk-target { font-size: 0.92rem; color: var(--ink-secondary); }
.vk-target b { color: var(--ink-primary); }
.vk-grid { display: grid; grid-template-columns: repeat(6, minmax(0, 1fr)); gap: 6px; }
.vk-key {
  min-height: 48px; min-width: 0; padding: 0 4px;
  display: inline-flex; align-items: center; justify-content: center;
  background: var(--bg-surface); color: var(--ink-primary);
  border: 1px solid var(--line-ui);
  border-radius: var(--radius-sm);
  box-shadow: 0 2px 0 var(--border-strong);
  cursor: pointer;
  user-select: none;
  -webkit-user-select: none;
  touch-action: manipulation;
  transition: transform var(--t-fast) var(--ease-tactile), background-color var(--t-fast) ease;
}
.vk-key:hover { background: var(--bg-hover); }
.vk-key:active { transform: translateY(2px); box-shadow: 0 0 0 var(--border-strong); }
.vk-key--math { font-size: 1.4rem; line-height: 1; }
.vk-key--var { background: var(--tile-var-bg); color: var(--tile-var-ink); }
.vk-key--word { font-size: 0.92rem; font-weight: 600; }
.vk-key--wide { grid-column: span 2; }
.vk-key sup { font-size: 0.75em; line-height: 0; vertical-align: 0.55em; margin-left: 1px; }
/* Kotak kosong di tombol pangkat digambar dengan CSS, bukan karakter, supaya tidak memanggil font lain. */
.vk-key .slot {
  display: inline-block; width: 0.55em; height: 0.7em;
  border: 2px solid var(--ink-secondary); border-radius: 2px;
}
.vk-toggle { min-height: 44px; }
.vk-off { margin-top: 12px; }

/* ---------- Latihan ---------- */
.practice { display: grid; grid-template-columns: minmax(0, 1fr); gap: 16px; }
@media (min-width: 820px) {
  .practice { grid-template-columns: 240px minmax(0, 1fr); align-items: start; gap: 24px; }
}
.levels ol { list-style: none; margin: 0; padding: 0; display: grid; gap: 8px; }
.level-btn {
  width: 100%;
  display: grid; gap: 2px; text-align: left;
  padding: 10px 14px; min-height: 56px;
  border-radius: var(--radius-md);
  border: 1px solid var(--line-ui);
  background: var(--bg-surface);
  cursor: pointer;
  transition: background-color var(--t-fast) ease;
}
.level-btn:hover { background: var(--bg-subtle); }
.level-btn .lv-name { font-weight: 700; }
.level-btn .lv-desc { font-size: 0.9rem; color: var(--ink-secondary); }
.level-btn .lv-prog { font-size: 0.85rem; color: var(--ink-secondary); }
.level-btn[aria-current="step"] { border: 2px solid var(--brand); background: var(--brand-soft); }
.level-btn[aria-current="step"] .lv-name { color: var(--brand-text); }
@media (max-width: 819px) {
  /* Di layar sempit tahap menjadi satu baris lima tombol, deskripsinya pindah ke kepala soal. */
  .levels ol { grid-template-columns: repeat(5, minmax(0, 1fr)); gap: 6px; }
  .level-btn { padding: 6px 4px; min-height: 52px; text-align: center; justify-items: center; align-content: center; }
  .level-btn .lv-desc { display: none; }
  .level-btn .lv-name { font-size: 0.85rem; }
  .level-btn .lv-prog { font-size: 0.8rem; }
}

.problem { min-width: 0; }
.problem-meta { color: var(--ink-secondary); font-weight: 600; font-size: 0.95rem; }
.problem h2 { font-size: 1.15rem; margin-top: 6px; }
.problem h2:focus { outline: none; }
.problem h2:focus-visible { outline: 3px solid var(--focus); outline-offset: 4px; }
.problem-expr { font-size: clamp(1.8rem, 1.3rem + 2.2vw, 2.4rem); margin: 8px 0 16px; overflow-wrap: anywhere; }

/* Jawaban ditulis seperti bentuk aslinya: [faktor depan] ( [isi kurung] ), dalam satu baris juga di ponsel. */
.answer-line {
  display: grid;
  grid-template-columns: minmax(72px, 1fr) auto minmax(0, 2.6fr) auto;
  align-items: end;
  column-gap: 4px;
}
.answer-line label { display: grid; gap: 4px; min-width: 0; font-weight: 600; font-size: 0.9rem; }
.answer-line .paren { font-size: 2.2rem; padding-bottom: 8px; color: var(--ink-primary); }
.answer-line .field { padding: 8px 8px; }

.preview {
  margin-top: 12px; padding: 10px 12px;
  border-radius: var(--radius-md);
  background: var(--bg-subtle);
  font-size: 0.98rem;
  overflow-wrap: anywhere;
}

fieldset.choices { border: 0; padding: 0; margin: 0; min-width: 0; }
.choice-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; }
@media (min-width: 560px) { .choice-list { grid-template-columns: repeat(4, minmax(0, 1fr)); } }
.choice { position: relative; }
.choice input { position: absolute; opacity: 0; width: 1px; height: 1px; }
.choice label {
  display: flex; align-items: center; justify-content: center;
  min-height: 56px; padding: 8px;
  font-size: 1.45rem;
  border: 1px solid var(--line-ui);
  border-radius: var(--radius-md);
  background: var(--bg-surface);
  box-shadow: var(--shadow-tactile-sm);
  cursor: pointer;
}
.choice label:hover { background: var(--bg-subtle); }
.choice input:checked + label {
  border: 2px solid var(--brand);
  background: var(--brand-soft);
  color: var(--brand-text);
}
.choice input:focus-visible + label { outline: 3px solid var(--focus); outline-offset: 2px; }

.actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 18px; align-items: center; }
.actions .spacer { flex: 1 1 0; }

.feedback {
  margin-top: 16px; padding: 14px 16px;
  border-radius: var(--radius-md);
  border: 1px solid;
  display: grid; gap: 6px;
}
.feedback .fb-title { font-weight: 700; }
.feedback--correct { background: var(--success-soft); border-color: var(--success-border); color: var(--success-text); }
.feedback--rethink { background: var(--accent-soft); border-color: var(--accent-border); color: var(--accent-text); }
.feedback--hint { background: var(--info-soft); border-color: var(--info-border); color: var(--info-text); }
.feedback--error { background: var(--danger-soft); border-color: var(--danger-border); color: var(--danger-text); }
.feedback ul { margin: 0; padding-left: 1.2em; }

.summary h2 { font-size: 1.3rem; }
.summary dl { display: grid; grid-template-columns: auto 1fr; gap: 6px 16px; margin: 14px 0 0; }
.summary dt { color: var(--ink-secondary); }
.summary dd { margin: 0; font-weight: 700; }

/* ---------- Pengantar ---------- */
.intro { display: grid; gap: 28px; }
@media (min-width: 860px) { .intro { grid-template-columns: minmax(0, 1.1fr) minmax(0, 1fr); align-items: start; } }
.intro h2 { font-size: 1.3rem; font-weight: 800; margin-bottom: 10px; }
.two-way { display: grid; gap: 10px; margin-top: 4px; }
.two-way .line {
  display: flex; flex-wrap: wrap; align-items: center; gap: 6px 12px;
  padding: 12px 14px; border-radius: var(--radius-md);
  background: var(--bg-surface); border: 1px solid var(--border-subtle);
}
.two-way .line .math { font-size: 1.5rem; }
.two-way .dir { font-size: 0.9rem; font-weight: 700; color: var(--ink-secondary); min-width: 7.5em; }
.two-way .line--focus { border: 2px solid var(--tile-common-border); background: var(--accent-soft); }
.two-way .line--focus .dir { color: var(--accent-text); }
.legend { list-style: none; margin: 0; padding: 0; display: grid; gap: 12px; }
.legend li { display: grid; grid-template-columns: 4.2rem minmax(0, 1fr); gap: 12px; align-items: center; }
.legend .tile { --stage-size: 1.35rem; justify-self: start; }
.steps-list { margin: 0; padding-left: 1.4em; display: grid; gap: 8px; }
.typing-help { display: grid; gap: 8px; }
.typing-help p { color: var(--ink-primary); }

@media (max-width: 480px) {
  .activity-box { padding: 12px; }
  .stage { padding: 18px 6px; min-height: 200px; --stage-size: 1.25rem; }
  .tile { min-width: 2.1rem; height: 2.4rem; padding: 0 6px; }
  .controls .btn, .actions .btn { flex: 1 1 auto; }
  .controls .spacer, .actions .spacer { display: none; }
  .vk { padding: 6px; }
  .vk-grid { gap: 5px; }
  .seg label { padding: 6px 10px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { transition-duration: 0ms !important; animation-duration: 0ms !important; }
}

.gap-s { margin-top: 12px; }
.gap-l { margin-top: 28px; }