:root {
  --bg: #f7f7fb;
  --card: #ffffff;
  --text: #22223b;
  --muted: #6b7280;
  --primary: #4f46e5;
  --primary-dark: #4338ca;
  --good: #16a34a;
  --bad: #dc2626;
  --border: #e5e7eb;
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}

.btn {
  display: inline-block;
  padding: 0.6rem 1.1rem;
  border-radius: 0.6rem;
  border: none;
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  text-decoration: none;
  text-align: center;
}
.btn.primary { background: var(--primary); color: white; }
.btn.primary:hover { background: var(--primary-dark); }
.btn.secondary { background: #eef2ff; color: var(--primary-dark); }
.btn.ghost { background: transparent; color: var(--muted); }

.gate {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 1rem;
}
.gate-card {
  background: var(--card);
  border-radius: 1rem;
  padding: 2.5rem;
  max-width: 24rem;
  width: 100%;
  text-align: center;
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.06);
}
.gate-card h1 { margin-top: 0; }
.error { color: var(--bad); font-size: 0.9rem; }

.app { max-width: 40rem; margin: 0 auto; padding: 1.5rem 1rem 3rem; }

.topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 1.5rem;
}
.topbar h1 { font-size: 1.4rem; margin: 0; }
.topbar-actions { display: flex; align-items: center; gap: 0.5rem; }

.feedback-menu { position: relative; }
.feedback-menu summary {
  list-style: none;
  cursor: pointer;
}
.feedback-menu summary::-webkit-details-marker { display: none; }
.feedback-menu[open] summary { background: #eef2ff; color: var(--primary-dark); border-radius: 0.6rem; }
.feedback-options {
  position: absolute;
  right: 0;
  top: calc(100% + 0.4rem);
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  box-shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
  padding: 0.4rem;
  display: flex;
  flex-direction: column;
  min-width: 12rem;
  z-index: 10;
}
.feedback-options a {
  padding: 0.5rem 0.7rem;
  border-radius: 0.4rem;
  color: var(--text);
  text-decoration: none;
  font-size: 0.9rem;
  white-space: nowrap;
}
.feedback-options a:hover { background: var(--bg); }

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 0.8rem;
  padding: 1.25rem;
}
.card h3 { margin-top: 0; }
.card label {
  display: block;
  margin-bottom: 0.75rem;
  font-size: 0.9rem;
  color: var(--muted);
}
.card input, .card select {
  display: block;
  width: 100%;
  margin-top: 0.25rem;
  padding: 0.5rem;
  border: 1px solid var(--border);
  border-radius: 0.4rem;
  font-size: 1rem;
}

.student-list { list-style: none; padding: 0; margin: 0 0 1.5rem; }
.student-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
  flex-wrap: wrap;
  padding: 0.9rem;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 0.6rem;
  margin-bottom: 0.6rem;
}
.student-actions { display: flex; gap: 0.4rem; flex-wrap: wrap; }
.empty { color: var(--muted); padding: 0.5rem 0; }

.back-btn { margin-bottom: 1rem; padding-left: 0; }

.practice-header {
  display: flex;
  align-items: baseline;
  justify-content: space-between;
  margin-bottom: 1rem;
}
.score { font-weight: 600; color: var(--muted); }

.flashcard {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 1rem;
  padding: 2rem 1.5rem;
  text-align: center;
}
.problem-text { font-size: 1.4rem; font-weight: 600; margin-bottom: 1.5rem; line-height: 1.4; }

#answer-form input {
  width: 100%;
  max-width: 16rem;
  padding: 0.7rem;
  font-size: 1.2rem;
  text-align: center;
  border: 2px solid var(--border);
  border-radius: 0.5rem;
  margin-bottom: 1rem;
}
#answer-form .actions { display: flex; gap: 0.75rem; justify-content: center; flex-wrap: wrap; }

.feedback { margin-top: 1rem; text-align: left; }
.feedback-text { font-weight: 600; text-align: center; }
.feedback-text.good { color: var(--good); }
.feedback-text.bad { color: var(--bad); }
.tutor-steps { padding-left: 1.4rem; }
.tutor-steps li { margin-bottom: 0.4rem; }
#next-btn { display: block; margin: 1rem auto 0; }

.topic-list { list-style: none; padding: 0; }
.topic-list li {
  padding: 0.6rem 0.9rem;
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 0.5rem;
  margin-bottom: 0.5rem;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #16161f;
    --card: #1f1f2b;
    --text: #e5e7eb;
    --muted: #9ca3af;
    --border: #33333f;
  }
}