:root {
  --bg: #0f172a;
  --panel: #1e293b;
  --panel-light: #273449;
  --text: #e2e8f0;
  --muted: #94a3b8;
  --accent: #38bdf8;
  --accent-dark: #0ea5e9;
  --border: #334155;
}

* { box-sizing: border-box; }

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

header {
  padding: 2rem 2rem 1rem;
  border-bottom: 1px solid var(--border);
}

header h1 {
  margin: 0 0 0.25rem;
  font-size: 1.6rem;
  letter-spacing: -0.02em;
}

.subtitle {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.tabs {
  display: flex;
  gap: 0.5rem;
  padding: 1rem 2rem 0;
}

.tab-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--muted);
  padding: 0.5rem 1.1rem;
  border-radius: 999px;
  cursor: pointer;
  font-size: 0.9rem;
  transition: all 0.15s ease;
}

.tab-btn:hover {
  color: var(--text);
  border-color: var(--accent);
}

.tab-btn.active {
  background: var(--accent);
  color: #062633;
  border-color: var(--accent);
  font-weight: 600;
}

main {
  padding: 1.5rem 2rem 3rem;
  max-width: 1100px;
  margin: 0 auto;
}

.tab-panel { display: none; }
.tab-panel.active { display: block; }

.cards {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 1rem;
  margin-bottom: 1.5rem;
}

.card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.1rem 1.3rem;
}

.card .value {
  font-size: 1.9rem;
  font-weight: 700;
  color: var(--accent);
}

.card .label {
  color: var(--muted);
  font-size: 0.85rem;
  margin-top: 0.2rem;
}

.info-box {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1rem 1.2rem;
  margin-bottom: 1.5rem;
  color: var(--text);
}

.toolbar {
  margin-bottom: 1rem;
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

.toolbar input {
  width: 100%;
  max-width: 320px;
  padding: 0.55rem 0.9rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  font-size: 0.9rem;
}

.toolbar input:focus {
  outline: none;
  border-color: var(--accent);
}

.btn-primary,
.btn-secondary,
.btn-danger {
  padding: 0.5rem 1rem;
  border-radius: 8px;
  border: 1px solid transparent;
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: all 0.15s ease;
}

.btn-primary {
  background: var(--accent);
  color: #062633;
}
.btn-primary:hover { background: var(--accent-dark); }

.btn-secondary {
  background: transparent;
  border-color: var(--border);
  color: var(--text);
}
.btn-secondary:hover { border-color: var(--accent); color: var(--accent); }

.btn-danger {
  background: transparent;
  border-color: #7f1d1d;
  color: #f87171;
}
.btn-danger:hover { background: #7f1d1d; color: #fecaca; }

.btn-small {
  padding: 0.3rem 0.65rem;
  font-size: 0.78rem;
  border-radius: 6px;
}

.actions-cell {
  display: flex;
  gap: 0.4rem;
  flex-wrap: wrap;
}

.entity-form {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 1.1rem 1.3rem;
  margin-bottom: 1.5rem;
}

.entity-form.hidden { display: none; }

.form-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 1rem;
}

.entity-form label {
  display: flex;
  flex-direction: column;
  gap: 0.35rem;
  font-size: 0.8rem;
  color: var(--muted);
}

.entity-form input,
.entity-form select {
  padding: 0.5rem 0.7rem;
  border-radius: 8px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-size: 0.9rem;
}

.entity-form input:focus,
.entity-form select:focus {
  outline: none;
  border-color: var(--accent);
}

.form-error {
  color: #f87171;
  font-size: 0.85rem;
  margin-top: 0.75rem;
  min-height: 1.1em;
}

.form-actions {
  margin-top: 1rem;
  display: flex;
  gap: 0.6rem;
}

.grade-select {
  padding: 0.3rem 0.5rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--bg);
  color: var(--text);
  font-size: 0.8rem;
}

table {
  width: 100%;
  border-collapse: collapse;
  background: var(--panel);
  border-radius: 10px;
  overflow: hidden;
}

thead th {
  text-align: left;
  background: var(--panel-light);
  color: var(--muted);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  padding: 0.7rem 1rem;
  border-bottom: 1px solid var(--border);
}

tbody td {
  padding: 0.65rem 1rem;
  border-bottom: 1px solid var(--border);
  font-size: 0.9rem;
}

tbody tr:last-child td { border-bottom: none; }
tbody tr:hover { background: var(--panel-light); }

.empty-row td {
  color: var(--muted);
  text-align: center;
  padding: 1.5rem;
}

.chart-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(320px, 1fr));
  gap: 1.25rem;
}

.chart-card {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.1rem 1.3rem 1.4rem;
}

.chart-card h3 {
  margin: 0 0 0.9rem;
  font-size: 0.95rem;
  color: var(--text);
  font-weight: 600;
}

.chart-card-wide {
  grid-column: 1 / -1;
}

.chart-canvas-wrap {
  position: relative;
  height: 260px;
}

.chart-canvas-wrap-small {
  height: 180px;
}

footer {
  text-align: center;
  color: var(--muted);
  font-size: 0.8rem;
  padding: 1rem 2rem 2rem;
}