/* ============================================================
   KARKA PHYSICS — SHELL
   Application-level layout: grid structure, column sizing,
   focus mode, responsive breakpoints.
   ============================================================ */

* { box-sizing: border-box; }

html, body {
  margin: 0;
  height: 100%;
  font-family: var(--font-sans);
  color: var(--color-ink);
  background: var(--color-bg-gradient);
}

button { font: inherit; }

/* ---------- App shell ---------- */
.app-shell {
  height: 100vh;
  display: grid;
  grid-template-columns: var(--rail-width-expanded) 1fr;
  gap: var(--space-xl);
  padding: var(--space-xl);
  overflow: hidden;
  transition:
    grid-template-columns var(--duration-base) var(--ease),
    gap var(--duration-base) var(--ease);
}

.app-shell.rail-collapsed {
  grid-template-columns: var(--rail-width-collapsed) 1fr;
}

.app-shell.full-visual {
  grid-template-columns: 0 1fr;
  gap: 0;
}

.app-shell.full-visual .left-rail {
  opacity: 0;
  pointer-events: none;
  transform: translateX(-18px);
}

/* ---------- Main panel ---------- */
.main-panel {
  display: flex;
  flex-direction: column;
  min-width: 0;
  min-height: 0;
}

.lesson-header {
  display: flex;
  justify-content: space-between;
  gap: var(--space-lg);
  align-items: flex-start;
  margin-bottom: 14px;
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--space-md);
}

/* ---------- Tabs row ---------- */
.subtopic-tabs,
.stage-tabs {
  display: grid;
  gap: 10px;
  margin-bottom: var(--space-md);
}

.subtopic-tabs {
  grid-template-columns: repeat(4, 1fr);
}

.stage-tabs {
  grid-template-columns: 1fr 1.45fr 1.1fr 1fr 1fr;
  width: 100%;
  align-items: center;
}

/* ---------- Content grid ---------- */
.content-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr) var(--teacher-column-width);
  gap: var(--space-lg);
  min-height: 0;
  flex: 1;
  margin-top: 2px;
  transition: grid-template-columns var(--duration-base) var(--ease);
}

/* ---------- Focus-graph mode ---------- */
body.focus-graph {
  overflow: hidden;
}

body.focus-graph .teacher-card {
  display: none;
}

body.focus-graph .content-grid {
  grid-template-columns: 1fr;
}

body.focus-graph .visual-card {
  position: fixed;
  inset: 18px;
  z-index: 9999;
  margin: 0;
  padding: 22px;
  display: flex;
  flex-direction: column;
  background: var(--color-panel);
  border-radius: 28px;
  box-shadow: var(--shadow-elevated);
  overflow: hidden;
}

body.focus-graph .visual-topbar {
  flex: 0 0 auto;
  margin-bottom: var(--space-md);
}

body.focus-graph .viz-scroll-wrap {
  flex: 1 1 auto;
  min-height: 0;
  overflow: auto;
  border-radius: var(--radius-xl);
}

body.focus-graph .viz-scroll-btn {
  display: none;
}

body.focus-graph .lesson-header,
body.focus-graph .subtopic-tabs,
body.focus-graph .stage-tabs,
body.focus-graph .left-rail {
  pointer-events: none;
}

body.focus-graph .stage-tabs,
body.focus-graph .subtopic-tabs {
  margin-bottom: var(--space-sm);
}

/* ---------- Responsive ---------- */
@media (max-width: 1380px) {
  .stage-tabs {
    grid-template-columns: 0.95fr 1.55fr 1.05fr 0.95fr 0.95fr;
    gap: var(--space-sm);
  }
}

@media (max-width: 1180px) {
  .stage-tabs {
    grid-template-columns: repeat(5, minmax(96px, 1fr));
    overflow-x: auto;
    padding-bottom: var(--space-xs);
  }
}

@media (max-width: 1050px) {
  .app-shell {
    grid-template-columns: 1fr;
    height: auto;
    overflow: auto;
  }
  .left-rail { display: none; }
  .content-grid { grid-template-columns: 1fr; }
  .subtopic-tabs { grid-template-columns: 1fr 1fr; }
  .lesson-header { flex-direction: column; }
  .progress-pill { white-space: normal; }
  .teacher-card { order: 2; }
  .visual-actions { flex-wrap: wrap; }
}

@media (max-height: 760px) {
  body.focus-graph #viz { min-height: 620px; }
}