:root {
  --accent: #0066ff;
  --accent-light: #3385ff;
  --text-color: #222;
  --bg-color: #ffffff;
  --header-height: 64px;
  --max-width: 900px;
}

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

body {
  font-family: "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg-color);
  color: var(--text-color);
  line-height: 1.6;
}

/* Header */
.app-header {
  background: var(--accent);
  color: #fff;
  height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 1.5rem;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
  position: sticky;
  top: 0;
  z-index: 1000;
}

.logo {
  font-weight: 600;
  font-size: 1.25rem;
}

.nav-links a {
  color: #fff;
  margin-left: 1rem;
  text-decoration: none;
  font-weight: 500;
  position: relative;
}

.nav-links a::after {
  content: "";
  position: absolute;
  bottom: -4px;
  left: 0;
  width: 0;
  height: 2px;
  background: #fff;
  transition: width 0.25s ease;
}

.nav-links a:hover::after,
.nav-links a:focus::after {
  width: 100%;
}

.nav-links a.active {
  font-weight: 700;
  text-decoration: underline;
}

/* Content */
.content {
  max-width: var(--max-width);
  margin: 2rem auto 4rem;
  padding: 0 1rem;
  opacity: 0;
}

/* Typography converted from Markdown */
.content h1 {
  font-size: 2rem;
  margin: 1.5rem 0 1rem;
  color: var(--accent);
}

.content h2 {
  font-size: 1.5rem;
  margin: 1.25rem 0 0.75rem;
  color: var(--accent);
}

.content h3 {
  font-size: 1.25rem;
  margin: 1rem 0 0.5rem;
  color: var(--accent-light);
}

.content p {
  margin: 0.75rem 0;
}

.content ul,
.content ol {
  margin: 0.75rem 0 0.75rem 1.25rem;
}

/* Footer */
.app-footer {
  text-align: center;
  font-size: 0.875rem;
  padding: 1.5rem;
  background: #f7f9fc;
  color: #555;
}

/* Fade-in animation */
.fade-in {
  animation: fadeInUp 0.5s ease-out forwards;
}

@keyframes fadeInUp {
  0% {
    opacity: 0;
    transform: translateY(16px);
  }
  100% {
    opacity: 1;
    transform: translateY(0);
  }
}

/* Loader spinner */
.loader {
  position: fixed;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  width: 48px;
  height: 48px;
  border: 5px solid #e1e4f0;
  border-top-color: var(--accent);
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
  z-index: 2000;
}

@keyframes spin {
  to {
    transform: translate(-50%, -50%) rotate(360deg);
  }
}

.hidden {
  display: none;
}