body {
  background: #1e1e2f;
  color: #fff;
  font-family: Arial, sans-serif;
  margin: 0;
}

a {
  color: #8f95b2;
  text-decoration: none;
}

.site-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  background: #2b2b3c;
  padding: 20px 30px;
}

.site-header .logo a {
  font-size: 1.6em;
  font-weight: bold;
  color: #fff;
}

.site-nav a {
  margin-left: 20px;
}

.nickname-box {
  background: #3c3c4d;
  padding: 5px 10px;
  border-radius: 5px;
}

.nickname-box button {
  margin-left: 10px;
  background: #8f95b2;
  color: #000;
  border: none;
  padding: 5px 10px;
  cursor: pointer;
}

.lesson-page {
  display: flex;
  flex-wrap: wrap;
  margin: 20px;
}

.sidebar-left,
.sidebar-right {
  flex: 1 1 200px;
  padding: 10px;
}

.sidebar-left {
  display: flex;
  flex-direction: column;
}

.sidebar-left h3 {
  margin-bottom: 15px;
}

.sidebar-left .sidebar-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  grid-template-rows: repeat(2, auto);
  gap: 10px;
}

.sidebar-left .lesson-item {
  background: #2b2b3c;
  border-radius: 8px;
  overflow: hidden;
  transition: transform 0.3s;
}

.sidebar-left .lesson-item:hover {
  transform: scale(1.05);
}

.sidebar-left .lesson-item img {
  width: 100%;
  display: block;
}

.sidebar-left .lesson-item p {
  margin: 5px 10px 10px 10px;
  text-align: center;
  font-size: 13px;
}

.lesson-main {
  flex: 2 1 600px;
  text-align: center;
  position: relative;
}

.iframe-container {
  position: relative;
  display: block;
  width: 100%;
  max-width: 100%;
}

.lesson-main iframe {
  width: 100%;
  height: 500px;
  max-width: none;
  border: none;
}

#fullscreenBtn {
  position: absolute;
  bottom: 10px;
  right: 10px;
  z-index: 20;
  padding: 8px 15px;
  cursor: pointer;
  background: #8f95b2;
  color: #000;
  border: none;
  border-radius: 5px;
}

#fullscreenBtn:hover {
  background: #a1a5c2;
}

.lesson-main .overlay {
  position: absolute;
  top: 0; left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0, 0, 0, 0.98);
  display: flex;
  align-items: center;
  justify-content: center;
  z-index: 10;
}

.lesson-main .overlay button {
  padding: 15px 30px;
  font-size: 18px;
  cursor: pointer;
  background: #8f95b2;
  color: #000;
  border: none;
  border-radius: 5px;
  transition: background 0.2s;
}

.lesson-main .overlay button:hover {
  background: #a1a5c2;
}

.ad-top,
.ad-bottom,
.ad-right {
  background: #444;
  color: #ccc;
  text-align: center;
  padding: 50px;
  margin: 20px;
}

.description-box {
  background: #2b2b3c;
  margin: 20px;
  padding: 20px;
  border-radius: 8px;
}

.site-footer {
  text-align: center;
  padding: 20px;
  background: #2b2b3c;
  color: #aaa;
}

.nickname-form {
  max-width: 400px;
  margin: 100px auto;
  text-align: center;
}

.nickname-form input {
  padding: 10px;
  margin: 10px 0;
  width: 80%;
}

.nickname-form button {
  padding: 10px 20px;
}

@media (max-width: 768px) {
  .lesson-page {
    flex-direction: column;
  }

  .sidebar-left .sidebar-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  .sidebar-left,
  .sidebar-right {
    flex: 1 1 100%;
  }

  .lesson-main iframe {
    height: auto;
  }
}

.index-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 20px;
  padding: 20px;
}

.index-item {
  background: #2b2b3c;
  padding: 10px;
  border-radius: 8px;
  transition: transform 0.3s;
}

.index-item:hover {
  transform: scale(1.05);
}

.index-item img {
  width: 100%;
  display: block;
  border-radius: 4px;
}

.index-item h3 {
  margin: 10px 0 0;
  text-align: center;
  font-size: 16px;
}


.login-container {
  max-width: 400px;
  margin: 100px auto;
  background: #2b2b3c;
  padding: 40px;
  border-radius: 8px;
  text-align: center;
}

.login-container h2 {
  margin-bottom: 20px;
}

.login-form input {
  width: 100%;
  padding: 12px;
  margin: 10px 0;
  border: none;
  border-radius: 5px;
}

.login-form button {
  width: 100%;
  padding: 12px;
  background: #8f95b2;
  color: #000;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}

.login-form button:hover {
  background: #a1a5c2;
}

.error {
  color: #f66;
  margin-bottom: 15px;
}

.admin-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 20px;
}

.admin-table th,
.admin-table td {
  border: 1px solid #444;
  padding: 12px;
  text-align: left;
}

.admin-table th {
  background: #3a3a4d;
  color: #fff;
}

.admin-table tr:nth-child(even) {
  background: #2b2b3c;
}

.admin-table tr:nth-child(odd) {
  background: #242434;
}

.admin-table a {
  color: #8f95b2;
  text-decoration: none;
}

.admin-table a:hover {
  text-decoration: underline;
}

.admin-btn {
  display: inline-block;
  margin: 10px 0;
  padding: 10px 20px;
  background: #8f95b2;
  color: #000;
  border-radius: 5px;
  text-decoration: none;
}

.admin-btn:hover {
  background: #a1a5c2;
}

.admin-form {
  max-width: 600px;
  background: #2b2b3c;
  padding: 30px;
  border-radius: 8px;
  margin: 50px auto;   /* ortalama */
  display: flex;
  flex-direction: column;
}

.admin-form label {
  margin: 10px 0 5px;
}

.admin-form input,
.admin-form textarea {
  padding: 10px;
  border: none;
  border-radius: 5px;
  width: 100%;
  margin-bottom: 15px;
  box-sizing: border-box;
}

.admin-form button {
  margin-top: 10px;
  padding: 12px 20px;
  background: #8f95b2;
  color: #000;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}

.admin-form button:hover {
  background: #a1a5c2;
}

.admin-btn {
  display: inline-block;
  margin: 20px auto; /* ortalı */
  padding: 8px 15px;
  background: #8f95b2;
  color: #000;
  border-radius: 5px;
  text-decoration: none;
}

.admin-btn:hover {
  background: #a1a5c2;
}

h1 {
  text-align: center;
}

.duration-box {
  background: #2b2b3c;
  color: #fff;
  padding: 10px 20px;
  border-radius: 5px;
  margin: 20px auto;
  max-width: 400px;
  text-align: center;
}
.leaderboard-box {
  background: #2b2b3c;
  color: #fff;
  padding: 20px;
  border-radius: 6px;
  margin: 40px auto;
  max-width: 600px;
}

.leaderboard-box h3 {
  margin-bottom: 15px;
}

.leaderboard-table {
  width: 100%;
  border-collapse: collapse;
}

.leaderboard-table th,
.leaderboard-table td {
  border: 1px solid #444;
  padding: 10px;
  text-align: left;
}

.leaderboard-table tr:nth-child(even) {
  background: #242434;
}

#leaderboard-modal {
  position: fixed;
  top: 80px;
  left: 50%;
  transform: translateX(-50%);
  background: #2b2b3c;
  color: #fff;
  padding: 20px;
  border-radius: 8px;
  max-width: 500px;
  z-index: 9999;
}

.lb-pages {
  margin-top: 15px;
  text-align: center;
}

.lb-pages button {
  margin: 0 5px;
  padding: 8px 15px;
  background: #8f95b2;
  color: #000;
  border: none;
  border-radius: 5px;
  cursor: pointer;
}

.lb-pages button:hover {
  background: #a1a5c2;
}

.leaderboard-table {
  width: 100%;
  border-collapse: collapse;
}

.leaderboard-table th,
.leaderboard-table td {
  border: 1px solid #444;
  padding: 10px;
}

.leaderboard-table tr:nth-child(even) {
  background: #242434;
}

.lb-close {
  float: right;
  background: transparent;
  border: none;
  color: #fff;
  font-size: 18px;
  cursor: pointer;
}

.lb-close:hover {
  color: #f66;
}