:root {
  --blue: #2456a6;
  --blue-dark: #163b73;
  --blue-light: #eaf1fc;
  --green: #2e8b57;
  --red: #c0392b;
  --gold: #c99a2e;
  --text: #22303f;
  --muted: #5b6b7c;
  --bg: #f5f7fa;
  --card-bg: #ffffff;
  --border: #dce3ec;
  --radius: 14px;
  --shadow: 0 2px 10px rgba(20, 40, 70, 0.08);
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  padding: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Segoe UI", "Helvetica Neue", Arial, sans-serif;
  font-size: 18px;
  line-height: 1.6;
}

.site-header {
  background: linear-gradient(135deg, var(--blue-dark), var(--blue));
  color: #fff;
  padding: 18px 20px;
  box-shadow: var(--shadow);
}
.header-inner {
  max-width: 980px;
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: baseline;
  flex-wrap: wrap;
  gap: 6px;
}
.brand-de { font-size: 1.5rem; font-weight: 700; margin-right: 10px; }
.brand-sub { font-size: 1rem; opacity: 0.85; }
.brand-ru { font-size: 1.15rem; opacity: 0.95; }

main#app {
  max-width: 980px;
  margin: 0 auto;
  padding: 24px 16px 60px;
  min-height: 60vh;
}

.site-footer {
  text-align: center;
  color: var(--muted);
  padding: 24px 16px 40px;
  font-size: 0.95rem;
}

/* ---------- Home: unit grid ---------- */
.intro-block {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px 22px;
  margin-bottom: 24px;
  box-shadow: var(--shadow);
}
.intro-block h2 { margin-top: 0; }
.intro-ru { margin-top: 10px; color: var(--muted); }

.unit-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 18px;
}

.unit-card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 20px;
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: transform 0.15s ease, box-shadow 0.15s ease;
  display: flex;
  flex-direction: column;
  gap: 8px;
  text-align: left;
}
.unit-card:hover, .unit-card:focus-visible {
  transform: translateY(-3px);
  box-shadow: 0 6px 20px rgba(20, 40, 70, 0.14);
}
.unit-card .unit-icon { font-size: 2rem; }
.unit-card h3 { margin: 0; font-size: 1.2rem; color: var(--blue-dark); }
.unit-card .unit-ru { color: var(--muted); font-size: 1rem; }
.unit-card .unit-desc { color: var(--text); font-size: 0.95rem; margin: 4px 0 0; }

.progress-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-top: 8px;
}
.progress-bar {
  flex: 1;
  height: 8px;
  background: var(--blue-light);
  border-radius: 6px;
  overflow: hidden;
}
.progress-bar-fill {
  height: 100%;
  background: var(--green);
  width: 0%;
  transition: width 0.3s ease;
}
.progress-label { font-size: 0.85rem; color: var(--muted); white-space: nowrap; }

/* ---------- Unit view ---------- */
.back-link {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  background: none;
  border: none;
  color: var(--blue);
  font-size: 1rem;
  cursor: pointer;
  padding: 6px 0;
  margin-bottom: 10px;
}
.back-link:hover { text-decoration: underline; }

.unit-header h2 { margin-bottom: 2px; }
.unit-header .unit-ru { color: var(--muted); font-size: 1.1rem; margin-bottom: 18px; }

.tabs {
  display: flex;
  gap: 6px;
  border-bottom: 2px solid var(--border);
  margin-bottom: 20px;
  overflow-x: auto;
}
.tab-btn {
  background: none;
  border: none;
  padding: 10px 16px;
  font-size: 1rem;
  cursor: pointer;
  color: var(--muted);
  border-bottom: 3px solid transparent;
  white-space: nowrap;
  font-family: inherit;
}
.tab-btn.active {
  color: var(--blue-dark);
  font-weight: 700;
  border-bottom-color: var(--blue);
}
.tab-btn:hover { color: var(--blue-dark); }

.tab-panel { animation: fadein 0.15s ease; }
@keyframes fadein { from { opacity: 0; } to { opacity: 1; } }

/* ---------- Spickzettel ---------- */
.spick-intro {
  background: var(--blue-light);
  border-radius: var(--radius);
  padding: 16px 18px;
  margin-bottom: 18px;
}
.spick-intro .ru { color: var(--muted); }
.spick-section {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
}
.spick-section h4 {
  margin: 0 0 4px;
  color: var(--blue-dark);
  font-size: 1.15rem;
}
.spick-section h4 .ru { display: block; font-size: 1rem; color: var(--muted); font-weight: 400; margin-top: 2px; }
.spick-point { margin: 12px 0; padding-top: 12px; border-top: 1px dashed var(--border); }
.spick-point:first-of-type { border-top: none; padding-top: 0; }
.spick-rule { font-weight: 600; }
.spick-rule-ru { color: var(--muted); margin-top: 3px; }
.spick-example {
  margin-top: 8px;
  background: var(--bg);
  border-left: 3px solid var(--gold);
  padding: 8px 12px;
  border-radius: 6px;
  font-style: italic;
}
.spick-example-ru {
  margin-top: 6px;
  color: var(--muted);
  border-left: 3px solid var(--gold);
  padding: 8px 12px;
  border-radius: 6px;
  background: var(--bg);
}

/* ---------- Flashcards ---------- */
.flash-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 16px;
  flex-wrap: wrap;
  gap: 10px;
}
.flash-controls .ru { color: var(--muted); }
.flash-counter { color: var(--muted); }
.flashcard-wrap {
  perspective: 1200px;
  max-width: 520px;
  margin: 0 auto 20px;
}
.flashcard {
  position: relative;
  height: 260px;
  cursor: pointer;
  transform-style: preserve-3d;
  transition: transform 0.5s;
}
.flashcard.flipped { transform: rotateY(180deg); }
.flash-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  padding: 24px;
  text-align: center;
  gap: 10px;
}
.flash-front {
  background: var(--card-bg);
  border: 2px solid var(--blue);
}
.flash-front .flash-main { font-size: 1.5rem; font-weight: 700; color: var(--blue-dark); }
.flash-back {
  background: var(--blue-dark);
  color: #fff;
  transform: rotateY(180deg);
}
.flash-back .flash-main { font-size: 1.4rem; font-weight: 700; }
.flash-note { font-size: 0.95rem; opacity: 0.9; }
.flash-hint { font-size: 0.85rem; color: var(--muted); }

.flash-nav {
  display: flex;
  justify-content: center;
  gap: 12px;
  margin-top: 4px;
}

/* ---------- Buttons ---------- */
.btn {
  background: var(--blue);
  color: #fff;
  border: none;
  border-radius: 8px;
  padding: 10px 20px;
  font-size: 1rem;
  cursor: pointer;
  font-family: inherit;
}
.btn:hover { background: var(--blue-dark); }
.btn.secondary {
  background: var(--card-bg);
  color: var(--blue);
  border: 1px solid var(--blue);
}
.btn.secondary:hover { background: var(--blue-light); }
.btn:disabled { opacity: 0.4; cursor: not-allowed; }

/* ---------- Exercises ---------- */
.exercise {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 18px 20px;
  margin-bottom: 18px;
  box-shadow: var(--shadow);
}
.exercise-num { color: var(--muted); font-size: 0.9rem; margin-bottom: 4px; }
.exercise-q { font-weight: 600; margin-bottom: 10px; }
.exercise input[type="text"], .exercise textarea {
  width: 100%;
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 12px;
  font-size: 1rem;
  font-family: inherit;
  margin-bottom: 8px;
}
.exercise textarea { min-height: 90px; resize: vertical; }
.mc-options { display: flex; flex-direction: column; gap: 8px; margin-bottom: 8px; }
.mc-option {
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 10px 14px;
  cursor: pointer;
  background: var(--bg);
}
.mc-option:hover { background: var(--blue-light); }
.mc-option.selected { border-color: var(--blue); background: var(--blue-light); }
.mc-option.correct { border-color: var(--green); background: #e8f6ee; }
.mc-option.incorrect { border-color: var(--red); background: #fbeceb; }

.feedback { margin-top: 8px; padding: 10px 12px; border-radius: 8px; font-size: 0.95rem; }
.feedback.correct { background: #e8f6ee; color: var(--green); }
.feedback.incorrect { background: #fbeceb; color: var(--red); }
.feedback .ru { display: block; margin-top: 4px; color: var(--muted); }

.sample-solution {
  margin-top: 10px;
  background: var(--blue-light);
  border-radius: 8px;
  padding: 10px 12px;
  display: none;
}
.sample-solution.shown { display: block; }
.sample-solution .ru { margin-top: 6px; color: var(--muted); }

/* ---------- Quiz ---------- */
.quiz-progress { color: var(--muted); margin-bottom: 14px; }
.quiz-score {
  text-align: center;
  padding: 30px 20px;
}
.quiz-score .big-score { font-size: 3rem; font-weight: 700; color: var(--blue-dark); }
.quiz-score-msg { font-size: 1.2rem; margin: 8px 0 4px; }
.quiz-score-msg-ru { color: var(--muted); }

@media (max-width: 600px) {
  body { font-size: 16.5px; }
  .flashcard { height: 300px; }
  .brand-de { font-size: 1.3rem; }

  /* Auf schmalen Bildschirmen (z.B. iPhone) ragte der 4. Tab ("Quiz") unsichtbar
     über den Rand hinaus und war nur durch Wischen erreichbar. Feste 2x2-Anordnung
     macht alle vier Tabs sofort sichtbar, ohne Scrollen. */
  .tabs {
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    overflow-x: visible;
    gap: 2px;
  }
  .tab-btn {
    padding: 10px 6px;
    font-size: 0.92rem;
    text-align: center;
    white-space: normal;
  }
}