/* SECTION 1: KVS TOKENS */
:root {
  color-scheme: light;

  --kvs-font-sans: "Noto Sans JP", "Hiragino Kaku Gothic ProN", "Yu Gothic",
    "Meiryo", ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont,
    "Segoe UI", sans-serif;
  --kvs-font-mono: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono",
    monospace;

  --kvs-color-page: #f7f7f5;
  --kvs-color-surface: #ffffff;
  --kvs-color-text: #18181b;
  --kvs-color-heading: #111827;
  --kvs-color-muted: #52525b;
  --kvs-color-kicker: #71717a;
  --kvs-color-border: rgb(9 9 11 / 12%);
  --kvs-color-border-strong: rgb(9 9 11 / 20%);
  --kvs-color-action-primary: #2456d6;
  --kvs-color-action-primary-hover: #1f49bc;
  --kvs-color-action-neutral-container: #eef2f7;
  --kvs-color-action-neutral-container-hover: #e2e8f0;
  --kvs-color-focus: #b8d4ff;

  --kvs-space-1: 4px;
  --kvs-space-2: 8px;
  --kvs-space-3: 12px;
  --kvs-space-4: 16px;
  --kvs-space-5: 20px;
  --kvs-space-6: 24px;
  --kvs-space-8: 32px;

  --kvs-radius-control: 6px;
  --kvs-radius-panel: 8px;
  --kvs-size-control-min: 44px;
  --kvs-leading-body: 1.72;

  --app-shell-width: 1080px;
}

* {
  box-sizing: border-box;
}

html {
  background: var(--kvs-color-page);
}

body {
  margin: 0;
  color: var(--kvs-color-text);
  font-family: var(--kvs-font-sans);
  line-height: var(--kvs-leading-body);
}

button,
select,
input {
  font: inherit;
}

/* SECTION 2: SCREEN SHELL */
.app-header,
.control-panel,
.kvs-print-sheet {
  width: min(100% - 32px, var(--app-shell-width));
  margin-inline: auto;
}

.app-header {
  display: grid;
  grid-template-columns: minmax(0, 1fr) auto;
  gap: var(--kvs-space-6);
  align-items: end;
  padding-block: 40px var(--kvs-space-5);
  border-block-end: 1px solid var(--kvs-color-border);
}

.app-header h1,
.exercise-set h2,
.problem-item h3,
.text-block h4 {
  margin: 0;
  color: var(--kvs-color-heading);
  letter-spacing: 0;
}

.app-header h1 {
  font-size: 2.6rem;
  line-height: 1.05;
}

.app-kicker,
.problem-id {
  margin: 0;
  color: var(--kvs-color-kicker);
  font-size: 0.82rem;
  font-weight: 760;
  letter-spacing: 0;
  line-height: 1.2;
  text-transform: uppercase;
}

.app-lead,
.control-note,
.exercise-set__heading p,
.problem-meta {
  margin: 0;
  color: var(--kvs-color-muted);
}

.app-lead {
  max-inline-size: 68ch;
  font-size: 1.02rem;
}

/* SECTION 3: SCREEN CONTROLS */
.control-panel {
  display: flex;
  flex-wrap: wrap;
  gap: var(--kvs-space-4);
  align-items: end;
  padding-block: var(--kvs-space-5);
}

.control-field,
.mode-field {
  display: grid;
  gap: var(--kvs-space-2);
}

.control-field span,
.mode-field legend {
  color: var(--kvs-color-muted);
  font-size: 0.82rem;
  font-weight: 700;
}

.control-field select {
  min-block-size: var(--kvs-size-control-min);
  border: 1px solid var(--kvs-color-border);
  border-radius: var(--kvs-radius-control);
  background: var(--kvs-color-surface);
  color: var(--kvs-color-text);
  padding-inline: var(--kvs-space-3);
}

.mode-field {
  grid-auto-flow: column;
  align-items: center;
  border: 1px solid var(--kvs-color-border);
  border-radius: var(--kvs-radius-control);
  padding: var(--kvs-space-2) var(--kvs-space-3);
}

.mode-field label {
  display: inline-flex;
  gap: var(--kvs-space-1);
  align-items: center;
  white-space: nowrap;
}

.control-note {
  margin-inline-start: auto;
  font-size: 0.92rem;
}

.kvs-button {
  min-block-size: var(--kvs-size-control-min);
  border: 1px solid var(--kvs-color-border);
  border-radius: var(--kvs-radius-control);
  background: var(--kvs-color-action-neutral-container);
  color: var(--kvs-color-text);
  cursor: pointer;
  font-weight: 760;
  padding-inline: var(--kvs-space-4);
}

.kvs-button--primary {
  border-color: transparent;
  background: var(--kvs-color-action-primary);
  color: #ffffff;
}

.kvs-button:hover {
  background: var(--kvs-color-action-neutral-container-hover);
}

.kvs-button--primary:hover {
  background: var(--kvs-color-action-primary-hover);
}

.kvs-button:focus-visible,
select:focus-visible,
input:focus-visible {
  outline: 3px solid var(--kvs-color-focus);
  outline-offset: 2px;
}

/* SECTION 4: EXERCISE CONTENT */
.kvs-print-sheet {
  display: grid;
  gap: var(--kvs-space-8);
  padding-block: var(--kvs-space-3) 56px;
}

.exercise-set {
  display: grid;
  gap: var(--kvs-space-5);
}

.exercise-set__heading {
  display: grid;
  gap: var(--kvs-space-2);
  border-block-end: 1px solid var(--kvs-color-border-strong);
  padding-block-end: var(--kvs-space-4);
}

.exercise-set h2 {
  font-size: 1.55rem;
}

.exercise-part {
  display: grid;
  gap: var(--kvs-space-4);
}

.exercise-part__heading {
  border-block-end: 1px solid var(--kvs-color-border);
  padding-block-end: var(--kvs-space-2);
}

.exercise-part__heading h3 {
  margin: 0;
  color: var(--kvs-color-heading);
  font-size: 1.22rem;
}

.exercise-part--answers {
  break-before: page;
}

.problem-item {
  display: grid;
  gap: var(--kvs-space-4);
  border: 1px solid var(--kvs-color-border);
  border-radius: var(--kvs-radius-panel);
  background: var(--kvs-color-surface);
  padding: var(--kvs-space-5);
}

.answer-item {
  border-style: dashed;
}

.problem-item__header {
  display: grid;
  grid-template-columns: auto minmax(0, 1fr) auto;
  gap: var(--kvs-space-4);
  align-items: start;
}

.question-number {
  display: grid;
  place-items: center;
  inline-size: 54px;
  block-size: 54px;
  border: 2px solid var(--kvs-color-border-strong);
  border-radius: var(--kvs-radius-control);
  color: var(--kvs-color-heading);
  font-size: 1.65rem;
  font-weight: 820;
  line-height: 1;
}

.problem-item h3 {
  margin-block-start: var(--kvs-space-1);
  font-size: 1.18rem;
  line-height: 1.35;
}

.problem-meta {
  display: flex;
  flex-wrap: wrap;
  justify-content: end;
  gap: var(--kvs-space-1);
  max-inline-size: 320px;
}

.problem-meta span {
  border: 1px solid var(--kvs-color-border);
  border-radius: var(--kvs-radius-control);
  padding: 2px var(--kvs-space-2);
  background: #fbfbfb;
  font-size: 0.78rem;
  font-weight: 700;
}

.text-block {
  display: grid;
  gap: var(--kvs-space-2);
}

.text-block h4 {
  font-size: 0.9rem;
}

.text-block__body {
  white-space: pre-wrap;
}

.solution-panel {
  display: grid;
  gap: var(--kvs-space-4);
}

body[data-explanation="off"] .explanation-body {
  display: none;
}

/* SECTION 5: KVS PRINT PRIMITIVES */
.kvs-print-section {
  break-inside: auto;
}

.kvs-print-item {
  break-inside: auto;
  page-break-inside: auto;
}

.print-page-footer {
  display: none;
}

/* SECTION 6: RESPONSIVE SCREEN */
@media (max-width: 720px) {
  .app-header {
    grid-template-columns: 1fr;
  }

  .problem-item__header {
    grid-template-columns: auto minmax(0, 1fr);
  }

  .app-header {
    align-items: start;
  }

  .problem-meta {
    justify-content: start;
    max-inline-size: none;
  }

  .control-note {
    margin-inline-start: 0;
  }
}

/* SECTION 7: A4 PRINT */
@page {
  size: A4;
  margin: 12mm 12mm 14mm;
}

@media print {
  :root {
    --kvs-color-page: #ffffff;
    --kvs-color-surface: #ffffff;
    --kvs-color-text: #000000;
    --kvs-color-heading: #000000;
    --kvs-color-muted: #333333;
    --kvs-color-border: rgb(0 0 0 / 22%);
    --kvs-color-border-strong: rgb(0 0 0 / 44%);
    --kvs-leading-body: 1.55;
  }

  html,
  body {
    background: #ffffff;
  }

  body {
    font-size: 10.5pt;
  }

  .screen-only {
    display: none !important;
  }

  .kvs-print-sheet {
    width: 100%;
    gap: 8mm;
    padding: 0;
  }

  .exercise-set {
    gap: 5mm;
    break-after: auto;
  }

  .exercise-set + .exercise-set {
    break-before: page;
  }

  .exercise-set__heading {
    padding-block-end: 3mm;
  }

  .exercise-set h2 {
    font-size: 15pt;
  }

  .exercise-part {
    gap: 4mm;
  }

  .exercise-part__heading {
    padding-block-end: 2mm;
  }

  .exercise-part__heading h3 {
    font-size: 12pt;
  }

  .problem-item {
    gap: 3mm;
    border-color: var(--kvs-color-border-strong);
    border-radius: 0;
    padding: 4mm;
  }

  .problem-item h3 {
    font-size: 11.5pt;
  }

  .question-number {
    inline-size: 15mm;
    block-size: 15mm;
    border-width: 1.5pt;
    border-radius: 0;
    font-size: 18pt;
  }

  .problem-meta span {
    background: #ffffff;
    font-size: 8pt;
  }

  .text-block {
    gap: 1mm;
  }

  .text-block h4 {
    font-size: 9pt;
  }

  .solution-panel {
    gap: 2mm;
  }

}