* { box-sizing: border-box; }
body {
  font-family: -apple-system, Segoe UI, Roboto, Arial, sans-serif;
  background: #f4f5f7;
  margin: 0;
  color: #1f2430;
}
header {
  background: #1f2430;
  color: #fff;
  padding: 16px 20px;
}
header h1 { margin: 0 0 10px; font-size: 20px; }
nav button {
  background: transparent;
  border: 1px solid #566;
  color: #fff;
  padding: 8px 16px;
  margin-right: 8px;
  border-radius: 6px;
  cursor: pointer;
}
nav button.active { background: #3d7bfd; border-color: #3d7bfd; }
main { max-width: 640px; margin: 20px auto; padding: 0 16px; }
.tab { display: none; }
.tab.active { display: block; }
.card {
  background: #fff;
  border-radius: 10px;
  padding: 16px;
  margin-bottom: 16px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}
.hint { font-size: 13px; color: #667; margin: 6px 0; }
label { display: block; margin-bottom: 10px; font-size: 14px; font-weight: 600; }
input, select, textarea {
  width: 100%;
  padding: 8px;
  margin-top: 4px;
  border: 1px solid #ccd;
  border-radius: 6px;
  font-size: 14px;
  font-weight: normal;
}
button[type="submit"], .action-btn {
  background: #3d7bfd;
  color: #fff;
  border: none;
  padding: 10px 16px;
  border-radius: 6px;
  cursor: pointer;
  font-size: 14px;
  margin-top: 6px;
}
.action-btn.secondary { background: #8a94a6; }
.action-btn.danger { background: #d64545; }
.date-chip {
  display: inline-block;
  background: #eef1f8;
  border: 1px solid #ccd;
  border-radius: 14px;
  padding: 4px 10px;
  margin: 4px 4px 0 0;
  cursor: pointer;
  font-size: 13px;
}
.student-card {
  background: #fff;
  border-radius: 10px;
  padding: 14px;
  margin-bottom: 10px;
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}
.student-card h3 { margin: 0 0 4px; }
.student-card .meta { font-size: 13px; color: #667; margin-bottom: 8px; }
.student-card .actions button { margin-right: 6px; margin-top: 6px; }