:root {
  --bg: #f4f7fb;
  --surface: #ffffff;
  --ink: #1f2937;
  --muted: #64748b;
  --line: #d9e2ec;
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --accent: #0f766e;
  --accent-soft: #d9f6f2;
  --danger: #b91c1c;
  --danger-soft: #fee2e2;
  --shadow: 0 18px 45px rgba(31, 41, 55, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: Arial, Helvetica, sans-serif;
  color: var(--ink);
  background:
    linear-gradient(135deg, rgba(37, 99, 235, 0.11), transparent 42%),
    linear-gradient(315deg, rgba(15, 118, 110, 0.13), transparent 38%),
    var(--bg);
}

button,
input {
  font: inherit;
}

.app-shell {
  width: min(1100px, calc(100% - 32px));
  margin: 0 auto;
  padding: 48px 0;
}

.tracker {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: 8px;
  box-shadow: var(--shadow);
  overflow: hidden;
}

.tracker__header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 24px;
  padding: 28px;
  background: #172033;
  color: #ffffff;
}

.eyebrow {
  margin: 0 0 8px;
  color: #b9e6df;
  font-size: 0.78rem;
  font-weight: 700;
  letter-spacing: 0;
  text-transform: uppercase;
}

h1,
h2,
p {
  margin-top: 0;
}

h1 {
  margin-bottom: 0;
  font-size: 3rem;
  line-height: 1;
  letter-spacing: 0;
}

h2 {
  margin-bottom: 0;
  font-size: 1.35rem;
}

.average-panel {
  min-width: 170px;
  padding: 16px 18px;
  border: 1px solid rgba(255, 255, 255, 0.28);
  border-radius: 8px;
  background: rgba(255, 255, 255, 0.08);
  text-align: right;
}

.average-panel span {
  display: block;
  margin-bottom: 6px;
  color: #dbeafe;
  font-size: 0.9rem;
}

.average-panel strong {
  display: block;
  font-size: 2rem;
  line-height: 1;
}

.student-form {
  display: grid;
  grid-template-columns: minmax(180px, 1fr) minmax(150px, 220px) auto;
  gap: 16px;
  align-items: end;
  padding: 24px 28px 12px;
}

.field {
  display: grid;
  gap: 8px;
}

label {
  color: var(--muted);
  font-size: 0.95rem;
  font-weight: 700;
}

input {
  width: 100%;
  min-height: 46px;
  border: 1px solid var(--line);
  border-radius: 6px;
  padding: 0 14px;
  color: var(--ink);
  background: #ffffff;
}

input:focus {
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37, 99, 235, 0.16);
  outline: none;
}

.primary-button,
.delete-button {
  min-height: 46px;
  border: 0;
  border-radius: 6px;
  font-weight: 700;
  cursor: pointer;
}

.primary-button {
  padding: 0 20px;
  color: #ffffff;
  background: var(--primary);
}

.primary-button:hover,
.primary-button:focus-visible {
  background: var(--primary-dark);
}

.delete-button {
  padding: 0 14px;
  color: var(--danger);
  background: var(--danger-soft);
}

.delete-button:hover,
.delete-button:focus-visible {
  color: #ffffff;
  background: var(--danger);
}

.error-message {
  min-height: 24px;
  margin: 0;
  padding: 0 28px 12px;
  color: var(--danger);
  font-weight: 700;
}

.student-section {
  padding: 16px 28px 30px;
}

.student-section__heading {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  margin-bottom: 14px;
}

#studentCount {
  color: var(--muted);
  font-weight: 700;
}

.table-wrap {
  overflow-x: auto;
  border: 1px solid var(--line);
  border-radius: 8px;
}

table {
  width: 100%;
  min-width: 620px;
  border-collapse: collapse;
}

th,
td {
  padding: 14px 16px;
  border-bottom: 1px solid var(--line);
  text-align: left;
}

th {
  color: var(--muted);
  font-size: 0.86rem;
  text-transform: uppercase;
}

tbody tr:last-child td {
  border-bottom: 0;
}

tbody tr.above-average {
  background: var(--accent-soft);
}

.badge {
  display: inline-flex;
  align-items: center;
  min-height: 28px;
  border-radius: 999px;
  padding: 0 10px;
  color: var(--muted);
  background: #eef2f7;
  font-size: 0.85rem;
  font-weight: 700;
  white-space: nowrap;
}

.badge--above {
  color: var(--accent);
  background: var(--accent-soft);
}

.empty-state {
  margin: 14px 0 0;
  color: var(--muted);
  text-align: center;
}

@media (max-width: 760px) {
  .app-shell {
    width: min(100% - 20px, 680px);
    padding: 20px 0;
  }

  .tracker__header,
  .student-form,
  .student-section__heading {
    align-items: stretch;
    flex-direction: column;
  }

  .tracker__header {
    padding: 22px;
  }

  h1 {
    font-size: 2.05rem;
  }

  .average-panel {
    width: 100%;
    text-align: left;
  }

  .student-form {
    grid-template-columns: 1fr;
    padding: 20px 22px 10px;
  }

  .error-message {
    padding-inline: 22px;
  }

  .student-section {
    padding: 14px 22px 24px;
  }
}