:root {
  --color-background-primary: #ffffff;
  --color-background-secondary: #f5f7fb;
  --color-background-info: #e6f1fb;
  --color-border-tertiary: #d8dee9;
  --color-border-secondary: #c9d3e0;
  --color-border-info: #90b9e9;
  --color-text-primary: #152033;
  --color-text-secondary: #5c6b80;
  --color-text-tertiary: #8a97aa;
  --color-text-info: #0c447c;
  --font-sans: "SF Pro Display", "PingFang SC", "Hiragino Sans GB", sans-serif;
  --font-serif: "Iowan Old Style", "STSong", serif;
  --font-mono: "SF Mono", "Menlo", monospace;
  --border-radius-md: 8px;
  --border-radius-lg: 8px;
  --shadow-soft: 0 16px 36px rgba(15, 23, 42, 0.08);
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--color-text-primary);
  background: var(--color-background-secondary);
}

button,
input,
select,
textarea {
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-md);
  background: var(--color-background-primary);
  color: var(--color-text-primary);
  font: inherit;
}

button {
  padding: 7px 12px;
  font-weight: 700;
  cursor: pointer;
}

input,
select,
textarea {
  padding: 7px 9px;
}

a {
  color: inherit;
}

.proof-shell {
  min-height: 100vh;
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
}

.proof-sidebar {
  padding: 28px 22px;
  border-right: 1px solid var(--color-border-tertiary);
  background: rgba(255, 255, 255, 0.88);
  backdrop-filter: blur(14px);
}

.proof-brand {
  margin-bottom: 28px;
}

.proof-brand__eyebrow,
.proof-section__eyebrow {
  margin: 0 0 8px;
  color: var(--color-text-info);
  font-size: 12px;
  font-weight: 800;
  text-transform: uppercase;
}

.proof-brand h1,
.proof-main__header h2,
.proof-section__header h3 {
  margin: 0;
}

.proof-brand p,
.proof-empty,
.proof-section__desc {
  color: var(--color-text-secondary);
  line-height: 1.6;
}

.proof-nav {
  display: grid;
  gap: 10px;
}

.proof-nav__item {
  border: 1px solid transparent;
  border-radius: var(--border-radius-md);
  background: transparent;
  color: var(--color-text-primary);
  padding: 12px 14px;
  text-align: left;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
}

.proof-nav__item.is-active,
.proof-nav__item:hover {
  background: var(--color-background-primary);
  border-color: var(--color-border-tertiary);
  box-shadow: 0 10px 20px rgba(15, 23, 42, 0.06);
}

.proof-main {
  padding: 28px;
}

.proof-main__header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  margin-bottom: 22px;
}

.proof-main__header p {
  margin: 8px 0 0;
  color: var(--color-text-secondary);
}

.proof-actions {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
}

.proof-button {
  border-radius: var(--border-radius-md);
  border: 1px solid var(--color-border-tertiary);
  background: var(--color-background-primary);
  color: var(--color-text-primary);
  padding: 11px 18px;
  font: inherit;
  font-weight: 700;
  cursor: pointer;
}

.proof-button--primary {
  background: #1f5fbf;
  border-color: transparent;
  color: white;
}

.proof-screen {
  display: none;
}

.proof-screen.is-active {
  display: block;
}

.proof-surface {
  background: rgba(255, 255, 255, 0.88);
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-lg);
  box-shadow: var(--shadow-soft);
  padding: 22px;
  margin-bottom: 18px;
}

.proof-section__header {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 12px;
  margin-bottom: 16px;
}

.proof-screen__content {
  display: grid;
  gap: 18px;
}

.proof-layout--two {
  display: grid;
  grid-template-columns: 1.15fr 1fr;
  gap: 18px;
}

.proof-frame {
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-lg);
  background: var(--color-background-primary);
  overflow: hidden;
  height: 560px;
}

.proof-frame iframe {
  width: 100%;
  height: 100%;
  border: none;
}

.proof-checklist {
  display: grid;
  gap: 12px;
}

.proof-checklist__item {
  display: block;
  padding: 14px;
  border-radius: var(--border-radius-md);
  background: var(--color-background-primary);
  border: 1px solid var(--color-border-tertiary);
  color: inherit;
  text-decoration: none;
}

a.proof-checklist__item:hover {
  border-color: var(--color-border-info);
  box-shadow: 0 10px 20px rgba(15, 23, 42, 0.06);
}

.proof-checklist__title {
  font-weight: 700;
  margin-bottom: 6px;
}

.proof-tag {
  display: inline-flex;
  padding: 4px 10px;
  border-radius: var(--border-radius-md);
  font-size: 12px;
  font-weight: 700;
  margin-right: 8px;
}

.proof-tag.student { background: #e6f1fb; color: #0c447c; }
.proof-tag.teacher { background: #eeedfe; color: #3c3489; }
.proof-tag.system { background: #eaf3de; color: #27500a; }

.proof-path-list {
  display: grid;
  gap: 10px;
}

.proof-path-list code {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 12px;
  background: #eef2f7;
  padding: 4px 8px;
  border-radius: var(--border-radius-md);
}

.proof-math-block {
  line-height: 1.7;
  white-space: normal;
  overflow-wrap: anywhere;
}

.proof-math-block .katex-display {
  overflow-x: auto;
  overflow-y: hidden;
  padding: 4px 0;
}

.proof-workbench {
  display: grid;
  gap: 14px;
}

.proof-workbench__hero {
  display: flex;
  justify-content: space-between;
  align-items: flex-start;
  gap: 16px;
  flex-wrap: wrap;
}

.proof-workbench__badges,
.proof-workbench__actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.proof-workbench__grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
}

.proof-workbench__grid--teacher {
  grid-template-columns: repeat(3, minmax(0, 1fr));
}

.proof-workbench__panel {
  margin-bottom: 0;
  min-height: 160px;
}

.proof-home-result__card {
  display: grid;
  gap: 8px;
  padding: 14px;
  border-radius: var(--border-radius-md);
  border: 1px solid var(--color-border-tertiary);
  background: var(--color-background-primary);
}

.proof-home-result__meta {
  font-size: 14px;
  font-weight: 700;
}

.proof-home-result__line {
  font-size: 12px;
  color: var(--color-text-secondary);
}

.proof-home-result__actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.proof-system-note {
  display: grid;
  gap: 8px;
  font-size: 13px;
  line-height: 1.6;
}

.proof-empty {
  padding: 10px 12px;
  border: 1px dashed var(--color-border-secondary);
  border-radius: var(--border-radius-md);
  background: var(--color-background-secondary);
}

@media (max-width: 1100px) {
  .proof-shell {
    grid-template-columns: 1fr;
  }

  .proof-sidebar {
    border-right: none;
    border-bottom: 1px solid var(--color-border-tertiary);
  }

  .proof-workbench__grid,
  .proof-workbench__grid--teacher {
    grid-template-columns: 1fr;
  }
}

.proof-view-body {
  min-height: 100vh;
  background: var(--color-background-secondary);
}

.proof-view-header {
  position: sticky;
  top: 0;
  z-index: 3;
  display: grid;
  grid-template-columns: auto minmax(220px, 1fr) minmax(280px, auto);
  gap: 18px;
  align-items: center;
  padding: 18px 24px;
  border-bottom: 1px solid var(--color-border-tertiary);
  background: rgba(255, 255, 255, 0.94);
  backdrop-filter: blur(12px);
}

.proof-view-header h1 {
  margin: 0;
  font-size: 22px;
}

.proof-view-header p {
  margin: 5px 0 0;
  color: var(--color-text-secondary);
}

.proof-back-link {
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-md);
  padding: 9px 12px;
  background: var(--color-background-primary);
  color: var(--color-text-primary);
  font-weight: 800;
  text-decoration: none;
}

.proof-view-tabs {
  display: flex;
  gap: 6px;
  flex-wrap: wrap;
  justify-content: flex-end;
}

.proof-view-tabs a {
  border: 1px solid var(--color-border-tertiary);
  border-radius: var(--border-radius-md);
  padding: 7px 10px;
  background: var(--color-background-primary);
  color: var(--color-text-secondary);
  font-size: 12px;
  font-weight: 700;
  text-decoration: none;
}

.proof-view-tabs a.is-active {
  background: var(--color-background-info);
  border-color: var(--color-border-info);
  color: var(--color-text-info);
}

.proof-view-main {
  width: 100%;
  margin: 0 auto;
  padding: 0;
}

@media (max-width: 1100px) {
  .proof-shell {
    grid-template-columns: 1fr;
  }

  .proof-sidebar {
    border-right: none;
    border-bottom: 1px solid var(--color-border-tertiary);
  }

  .proof-layout--two {
    grid-template-columns: 1fr;
  }

  .proof-view-header {
    grid-template-columns: 1fr;
    align-items: start;
  }

  .proof-view-tabs {
    justify-content: flex-start;
  }
}

@media (max-width: 760px) {
  .proof-main {
    padding: 18px;
  }

  .proof-main__header,
  .proof-section__header {
    display: grid;
  }

  .proof-frame {
    height: 620px;
  }
}