body {
  font-family: Arial, sans-serif;
  padding: 20px;
  display: flex;
  justify-content: center;
  background: #f9fafb;
}

.container {
  max-width: 650px;
  width: 100%;
  background: #fff;
  padding: 20px;
  border-radius: 12px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.1);
}

h2 {
  text-align: center;
  color: #2563eb;
  margin-bottom: 15px;
}

table {
  border-collapse: collapse;
  width: 100%;
  table-layout: fixed;
}

th,
td {
  border: 1px solid #ccc;
  padding: 8px;
  text-align: center;
  vertical-align: middle;
  font-size: 14px;
}

th {
  background-color: #e5e7eb;
}

select {
  width: 100%;
  padding: 5px;
  font-size: 14px;
  box-sizing: border-box;
  border-radius: 6px;
}

button {
  padding: 8px 12px;
  font-size: 14px;
  margin-top: 10px;
  cursor: pointer;
  border: none;
  border-radius: 6px;
  background: #2563eb;
  color: #fff;
}

button:hover {
  background: #1e40af;
}

.valid {
  background-color: #dcfce7;
}

.invalid {
  background-color: #fee2e2;
}

footer {
  margin-top: 15px;
  font-size: 13px;
  text-align: center;
  color: #444;
}

.author {
  font-weight: bold;
  color: #111;
}

/* 👇 Sabit “Yıl” sütunu */
th:first-child,
td:first-child {
  position: sticky;
  left: 0;
  background: #e5e7eb;
  z-index: 2;
}

td:first-child {
  position: sticky;
  left: 0;
  background: #ffffff; /* alt satırlar beyaz */
  z-index: 1;
}