body {
  font-family: Arial, sans-serif;
  background-color: #f0f2f5;
  margin: 0;
  padding: 0;
  color: #333;
}

header {
  background-color: #fff;
  padding: 15px 0;
  border-bottom: 1px solid #ddd;
}

nav ul {
  list-style: none;
  display: flex;
  justify-content: center;
  gap: 30px;
  margin: 0;
  padding: 0;
}

nav ul li a {
  text-decoration: none;
  color: #007bff;
  font-weight: bold;
}

.container {
  max-width: 800px;
  margin: 0 auto;
  padding: 30px 20px;
}

section {
  margin-bottom: 40px;
  text-align: center;
}

input[type="text"],
button {
  display: block;
  width: 70%;
  margin: 10px auto;
  padding: 10px;
  border-radius: 4px;
}

input[type="text"] {
  border: 1px solid #ccc;
}

button {
  background-color: #28a745;
  border: none;
  color: white;
  font-weight: bold;
  cursor: pointer;
}

button:disabled {
  background-color: #ccc;
  cursor: not-allowed;
}

.ad-banner {
  text-align: center;
}

.ad-placeholder {
  width: 100%;
  height: 90px;
  background: #ddd;
  line-height: 90px;
  text-align: center;
  font-weight: bold;
  border: 1px solid #aaa;
}

.popup {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(240, 242, 245, 0.95);
  z-index: 999;
  text-align: center;
  padding-top: 100px;
}

.popup h3 {
  margin-top: 0;
}

.close-btn {
  position: absolute;
  top: 20px;
  right: 30px;
  font-size: 24px;
  background: none;
  border: none;
  cursor: pointer;
}

.hidden {
  display: none;
}

footer {
  background-color: #fff;
  text-align: center;
  padding: 20px;
  border-top: 1px solid #ddd;
  font-size: 0.9em;
}