body {
  font-family: sans-serif;
  margin: 0;
  padding: 1rem;
  background: #000;
  color: #fff;
  display: flex;
  flex-direction: column;
  align-items: center;
}

.header {
  width: 100%;
  max-width: 700px;
  display: flex;
  justify-content: space-between;
  margin-bottom: 1rem;
  padding: 0 1rem;
}

h1 {
  font-size: 1.5rem;
}

button {
  background: #222;
  color: white;
  border: 1px solid #555;
  padding: 0.5rem 1rem;
  cursor: pointer;
}

button:hover {
  background: #333;
}

.bingo-card {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 5px;
  width: 100%;
  max-width: 700px;
}

.square {
  background: #222;
  border: 2px solid #555;
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 10px;
  cursor: pointer;
  user-select: none;
  word-break: break-word;
  aspect-ratio: 1 / 1;
}

.square:hover {
  background: #444;
}

.marked {
  background: #0a0;
  color: black;
  text-decoration: line-through;
}

.login-container {
  max-width: 400px;
  margin-top: 5rem;
  padding: 2rem;
  background: #111;
  border: 1px solid #555;
}

input {
  width: 100%;
  padding: 0.5rem;
  margin-bottom: 1rem;
  background: #222;
  color: #fff;
  border: 1px solid #555;
}

.back {
  position: absolute;
  top: 16px;
  left: 16px;
  padding: 6px 12px;
  background: #121826;
  border: 1px solid #202a3b;
  border-radius: 6px;
  color: #e6eaf2;
  text-decoration: none;
  font-size: 0.9rem;
  transition: background 0.2s, border-color 0.2s;
}

.back:hover {
  background: #1c2333;
  border-color: #4da6ff;
}