:root {
  --primary: #1b6e3c;
  --primary-dark: #124d29;
  --accent: #e8b600;
  --bg: #f4f7f5;
  --card-bg: #ffffff;
  --text: #222;
  --muted: #667;
  --border: #dde3df;

  --grade-A: #2e7d32;
  --grade-B: #66a832;
  --grade-C: #c8b400;
  --grade-D: #e08e00;
  --grade-E: #e05a00;
  --grade-F: #c62828;
}

* { box-sizing: border-box; }

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

.app-header {
  background: linear-gradient(135deg, var(--primary), var(--primary-dark));
  color: white;
  padding: 24px 20px;
  text-align: center;
}

.app-header h1 { margin: 0 0 6px; font-size: 1.6rem; }
.app-header p { margin: 0; opacity: 0.9; font-size: 0.95rem; }

.container {
  max-width: 900px;
  margin: 24px auto;
  padding: 0 16px 40px;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 20px 24px;
  margin-bottom: 20px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.05);
}

.card h2 { margin-top: 0; font-size: 1.15rem; color: var(--primary-dark); }
.card h3 { font-size: 1rem; color: var(--primary-dark); }

.muted { color: var(--muted); font-size: 0.88rem; }

.form-row {
  display: flex;
  gap: 16px;
  flex-wrap: wrap;
  align-items: flex-end;
  margin-bottom: 12px;
}

.form-group {
  display: flex;
  flex-direction: column;
  gap: 6px;
  flex: 1 1 200px;
}

.form-group-btn { flex: 0 0 auto; }

label { font-weight: 600; font-size: 0.85rem; }

select, input[type="number"], input[type="file"] {
  padding: 8px 10px;
  border: 1px solid var(--border);
  border-radius: 6px;
  font-size: 0.95rem;
  background: white;
}

button {
  background: var(--primary);
  color: white;
  border: none;
  padding: 10px 18px;
  border-radius: 6px;
  font-size: 0.95rem;
  cursor: pointer;
  font-weight: 600;
  transition: background 0.15s;
}

button:hover:not(:disabled) { background: var(--primary-dark); }
button:disabled { background: #a9b8ad; cursor: not-allowed; }

button.secondary {
  background: white;
  color: var(--primary-dark);
  border: 1px solid var(--primary);
}
button.secondary:hover { background: #eef6ef; }

.hidden { display: none !important; }

.result-box { margin-top: 14px; }

.error { color: #c62828; font-weight: 600; }

.grade-card {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 14px 18px;
  border-radius: 8px;
  border-left: 8px solid var(--primary);
  background: #f4f9f5;
}

.grade-letter {
  font-size: 2.2rem;
  font-weight: 800;
  min-width: 50px;
  text-align: center;
}

.grade-A { border-color: var(--grade-A); } .grade-A .grade-letter { color: var(--grade-A); }
.grade-B { border-color: var(--grade-B); } .grade-B .grade-letter { color: var(--grade-B); }
.grade-C { border-color: var(--grade-C); } .grade-C .grade-letter { color: var(--grade-C); }
.grade-D { border-color: var(--grade-D); } .grade-D .grade-letter { color: var(--grade-D); }
.grade-E { border-color: var(--grade-E); } .grade-E .grade-letter { color: var(--grade-E); }
.grade-F { border-color: var(--grade-F); } .grade-F .grade-letter { color: var(--grade-F); }

table {
  border-collapse: collapse;
  width: 100%;
  font-size: 0.9rem;
}

th, td {
  border: 1px solid var(--border);
  padding: 6px 10px;
  text-align: left;
}

th { background: #eef6ef; }

.table-scroll {
  overflow-x: auto;
  max-height: 400px;
  overflow-y: auto;
  border: 1px solid var(--border);
  border-radius: 6px;
}

.band-input { width: 100%; padding: 4px 6px; border: 1px solid var(--border); border-radius: 4px; }
.band-grade { text-align: center; font-weight: 700; }

.grade-cell.grade-A { background: #e8f5e9; }
.grade-cell.grade-B { background: #f1f8e9; }
.grade-cell.grade-C { background: #fffde7; }
.grade-cell.grade-D { background: #fff3e0; }
.grade-cell.grade-E { background: #fbe9e7; }
.grade-cell.grade-F { background: #ffebee; }

.student-group-start td { border-top: 2px solid var(--primary); }

.row-delete-btn {
  background: transparent;
  color: #c62828;
  border: none;
  font-size: 1.1rem;
  font-weight: 800;
  padding: 0 6px;
  cursor: pointer;
}
.row-delete-btn:hover { color: #7f1d1d; }


.app-footer {
  text-align: center;
  padding: 16px;
  color: var(--muted);
  font-size: 0.85rem;
}