:root {
  --primary-color: #3498db;
  --secondary-color: #2ecc71;
  --dark-color: #2c3e50;
  --light-color: #ecf0f1;
  --danger-color: #e74c3c;
  --youtube-color: #ff0000;
  --google-color: #4285f4;
}

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  line-height: 1.6;
  color: #333;
  background-color: #f4f4f4;
}

a {
  color: var(--primary-color);
  text-decoration: none;
}

ul {
  list-style: none;
}

.container {
  max-width: 1100px;
  margin: 0 auto;
  padding: 0 2rem;
  overflow: hidden;
}

header {
  background-color: var(--dark-color);
  color: #fff;
  padding: 2rem 0;
  text-align: center;
}

header h1 {
  font-size: 2.5rem;
  margin-bottom: 0.5rem;
}

.tutorial-nav {
  margin: 1rem 0;
  padding: 0.5rem 0;
  border-bottom: 1px solid #ddd;
}

.source-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(250px, 1fr));
  gap: 1rem;
  margin: 2rem 0;
}

.source-card {
  background: #fff;
  border-radius: 5px;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
  padding: 1.5rem;
  transition: transform 0.3s ease;
}

.source-card:hover {
  transform: translateY(-5px);
}

.source-card h3 {
  color: var(--dark-color);
  margin-bottom: 1rem;
  border-bottom: 2px solid var(--light-color);
  padding-bottom: 0.5rem;
}

.source-card ul li {
  margin: 0.5rem 0;
}

.tutorial-card {
  background: #fff;
  border-radius: 5px;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
  padding: 1.5rem;
  margin: 2rem 0;
}

.tutorial-card h3 {
  color: var(--dark-color);
  margin-bottom: 1rem;
}

.btn {
  display: inline-block;
  background: var(--primary-color);
  color: #fff;
  padding: 0.5rem 1.5rem;
  border: none;
  border-radius: 5px;
  margin-top: 1rem;
  cursor: pointer;
  transition: opacity 0.2s ease;
}

.btn:hover {
  opacity: 0.9;
}

.tags {
  margin-top: 1rem;
}

.tag {
  display: inline-block;
  font-size: 0.8rem;
  padding: 0.2rem 0.5rem;
  border-radius: 3px;
  margin-right: 0.5rem;
  color: #fff;
}

.tag.youtube {
  background: var(--youtube-color);
}

.tag.net-ninja {
  background: #9b59b6;
}

.tag.dart {
  background: #0175c2;
}

.tag.flutter {
  background: #02569b;
}

section {
  margin: 2rem 0;
}

section h2 {
  color: var(--dark-color);
  margin-bottom: 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--light-color);
}

footer {
  background: var(--dark-color);
  color: #fff;
  text-align: center;
  padding: 2rem 0;
  margin-top: 3rem;
}

@media (max-width: 700px) {
  .source-grid {
    grid-template-columns: 1fr;
  }
}