:root {
  --bg: #fafafa;
  --fg: #111;
  --accent: #4da3ff;
  --accent-strong: #3b89ff;
  --accent-light: #eaf4ff;
  --card-bg: #fff;
  --border: #ddd;
}

body {
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--fg);
  margin: 0;
  line-height: 1.6;
}

/* Header/Nav */
.site-header {
  background: #fff;
  border-bottom: 2px solid var(--border);
  padding: 1.4rem 0;
}

.nav-wrap {
  display: flex;
  align-items: center;
  justify-content: space-between;
}

.brand {
  font-size: 1.45rem;
  font-weight: 700;
  color: var(--accent-strong);
  letter-spacing: 0.3px;
  text-decoration: none;
  transition: color 0.2s ease-in-out;
}

.brand:hover {
  color: var(--accent);
}

.nav a {
  margin-left: 1.2rem;
  text-decoration: none;
  color: var(--fg);
  font-weight: 500;
  padding: 0.5rem 0.25rem;
  transition: color 0.2s ease-in-out;
}

.nav a:hover {
  color: var(--accent);
}

.nav a.active {
  border-bottom: 2px solid var(--accent);
  color: var(--accent-strong);
}

/* Layout */
.container {
  width: 90%;
  max-width: 1100px;
  margin: 2.8rem auto;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 2rem;
  margin-bottom: 3rem;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.05);
}

h1 {
  font-size: 1.9rem;
  margin-bottom: 1.5rem;
}

h2 {
  margin-top: 0;
  font-size: 1.35rem;
}

/* Buttons */
.btn {
  display: inline-block;
  background: var(--accent);
  color: white;
  padding: 0.65rem 1.1rem;
  border-radius: 6px;
  text-decoration: none;
  font-weight: 500;
  transition: background 0.2s ease-in-out;
}

.btn:hover {
  background: var(--accent-strong);
}

.btn.ghost {
  background: transparent;
  color: var(--accent-strong);
  border: 1px solid var(--accent);
}

.btn.ghost:hover {
  background: var(--accent-light);
}

/* Stack layouts */
.stack {
  display: flex;
  flex-direction: column;
  gap: 1.2rem;
}

/* PDF & Video */
.pdf-preview {
  width: 100%;
  aspect-ratio: 4/3;         /* ensures landscape slides stay landscape */
  height: auto;
  max-height: 80vh;
  border: none;
}

.video {
  width: 100%;
  border-radius: 8px;
  height: auto;
  max-height: 80vh;
  object-fit: contain;
}

/* Footer */
.site-footer {
  background: #fff;
  border-top: 2px solid var(--border);
  text-align: center;
  padding: 1.3rem;
  margin-top: 4rem;
}

.btn + .pdf-preview {
  margin-top: 1rem;
}

.pdf-preview {
  margin-top: 1rem;
  margin-bottom: 1rem;
}

/* Concordia modal */
.modal {
  display: none;
  position: fixed;
  z-index: 1000;
  inset: 0;
  background: rgba(0, 0, 0, 0.7);
  backdrop-filter: blur(4px);
  justify-content: center;
  align-items: center;
  animation: fadeIn 0.3s ease-in-out;
}

.modal-content {
  background: #fff;
  width: 90%;
  max-width: 1200px;
  height: 85vh;
  border-radius: 1rem;
  overflow: hidden;
  position: relative;
  box-shadow: 0 8px 30px rgba(0,0,0,0.3);
}

.modal-content iframe {
  width: 100%;
  height: 100%;
  border: none;
}

.close-btn {
  position: absolute;
  top: 12px;
  right: 18px;
  font-size: 32px;
  color: #333;
  cursor: pointer;
  transition: color 0.2s;
}

.close-btn:hover {
  color: #e11d48;
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

.preview {
  margin: 1.5rem 0;
  border-radius: 12px;
  overflow: hidden;
  border: 1px solid var(--border);
  box-shadow: 0 2px 10px rgba(0,0,0,0.08);
}

.preview-img {
  width: 50%;
  height: auto;
  display: block;
  transition: transform 0.4s ease, filter 0.4s ease;
  cursor: pointer;
}

.preview-img:hover {
  transform: scale(1.02);
  filter: brightness(1.05);
}

.preview.compact {
  width: 40%;
  margin: 1rem auto;
  border-radius: 10px;
  box-shadow: 0 2px 8px rgba(0, 0, 0, 0.06);
}

.preview.compact .preview-img {
  border-radius: 10px;
}

/* ----------------------------- */
/*   RESPONSIVE MOBILE LAYOUT    */
/* ----------------------------- */

@media (max-width: 700px) {

  /* Fix header spacing & wrapping */
  .nav-wrap {
    flex-direction: column;
    align-items: flex-start;
    gap: 0.8rem;
  }

  .nav {
    display: flex;
    flex-direction: column;
    gap: 0.4rem;
  }

  .nav a {
    margin: 0;
    font-size: 1.1rem;
  }

  .nav a.active {
    border-bottom-width: 2px;
    padding-bottom: 1px;
  }

  /* Adjust header height */
  .site-header {
    padding: 1rem 0 0.4rem;
  }

  /* PDF scaling */
  .pdf-preview {
    aspect-ratio: 4/3;
    max-height: 60vh;
  }

  /* Video */
  .video {
    max-height: 60vh;
    object-fit: contain;
  }

  /* Preview images */
  .preview-img {
    width: 100%;
  }

  .preview.compact {
    width: 90%;
  }
}