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

body {
  font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  background: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);
  color: #eee;
  padding: 20px;
}

.container {
  max-width: 1200px;
  margin: 0 auto;
}

h1 {
  font-size: 28px;
  text-align: center;
  margin-bottom: 10px;
}

.subtitle {
  text-align: center;
  color: #aaa;
  margin-bottom: 40px;
  font-size: 14px;
}

/* ===================================
           THEORY SECTION
           =================================== */
.theory {
  background-color: #0a0a1a;
  border-radius: 16px;
  padding: 25px;
  margin-bottom: 30px;
}

.theory h2 {
  color: #4a90e2;
  margin-bottom: 15px;
}

.theory h3 {
  color: #e94560;
  margin: 20px 0 10px;
}

.theory p {
  color: #ccc;
  line-height: 1.6;
  margin-bottom: 15px;
}

.theory ul {
  margin-left: 25px;
  color: #ccc;
  line-height: 1.8;
}

.theory code {
  background-color: #1a1a2e;
  padding: 2px 6px;
  border-radius: 4px;
  color: #82b1ff;
}

/* ===================================
           DEMO SECTIONS
           =================================== */
.demo-section {
  background-color: #0f3460;
  border-radius: 16px;
  padding: 25px;
  margin-bottom: 30px;
}

.demo-section h3 {
  color: #4a90e2;
  margin-bottom: 15px;
}

.demo-section p {
  color: #aaa;
  margin-bottom: 20px;
  line-height: 1.6;
}

.image-container {
  background-color: #1a1a2e;
  border-radius: 12px;
  padding: 20px;
  text-align: center;
}

img {
  max-width: 100%;
  height: auto;
  border-radius: 8px;
}

/* ===================================
           CODE BLOCK
           =================================== */
.code-block {
  background-color: #0a0a1a;
  padding: 20px;
  border-radius: 12px;
  font-family: "Courier New", monospace;
  font-size: 13px;
  color: #82b1ff;
  overflow-x: auto;
  margin-top: 20px;
}

/* ===================================
           BACKGROUND IMAGE DEMO
           =================================== */
.bg-demo {
  background-image: url("<https://picsum.photos/id/1015/400/300>");
  background-size: cover;
  background-position: center;
  height: 200px;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  font-weight: bold;
  text-shadow: 0 0 10px rgba(0, 0, 0, 0.5);
}

@media (min-width: 768px) {
  .bg-demo {
    background-image: url("<https://picsum.photos/id/1015/800/400>");
  }
}

@media (min-width: 1024px) {
  .bg-demo {
    background-image: url("<https://picsum.photos/id/1015/1200/500>");
  }
}

footer {
  text-align: center;
  padding: 30px;
  color: #666;
  font-size: 14px;
}

/* Placeholder image text */
.img-note {
  font-size: 12px;
  color: #888;
  margin-top: 10px;
}