:root{
  --accent: #2a6f97;       /* change to a subtle orange if you prefer: #d66a2a */
  --muted: #6b6b6b;
  --max-width: 820px;
  --sans: system-ui, -apple-system, "Segoe UI", Roboto, "Helvetica Neue", Arial;
}

html, body{
  height: 100%;
  font-family: var(--sans);
  color: #0b0b0b;
  background: #fbfbfb;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

.container{
  max-width: 960px;
}

/* HERO */
.hero{
  padding-top: 3.5rem;
  padding-bottom: 3.5rem;
}

.display-4{
  font-weight: 650;
  letter-spacing: -0.02em;
}

.lead{
  color: var(--muted);
  max-width: var(--max-width);
  font-size: 1.125rem;
  line-height: 1.6;
}

/* Book cover in hero */
.book-cover{
  width: 100%;
  max-width: 360px;
  height: auto;
  border-radius: 14px;
  background: #fff;
  border: 1px solid rgba(0,0,0,0.06);
  box-shadow: 0 10px 30px rgba(0,0,0,0.06);
}

/* Section titles */
.section-title{
  font-size: 0.95rem;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--muted);
  margin-bottom: 0.75rem;
}

.section-subtitle{
  font-size: 1.25rem;
  margin-bottom: 0.6rem;
  color: #111;
}

.muted-max-width{
  max-width: var(--max-width);
  color: var(--muted);
  margin-bottom: 0;
}

/* Lists */
.simple-list{
  list-style: none;
  padding-left: 0;
  color: var(--muted);
}
.simple-list li{
  margin-bottom: 0.35rem;
}

/* Testimonials */
.testimonial{
  max-width: 780px;
  margin: 1.25rem auto;
  font-style: italic;
  color: #222;
  border-left: 2px solid #eee;
  padding-left: 1rem;
}
.testimonial footer{
  margin-top: 0.5rem;
  font-style: normal;
  color: var(--muted);
}

/* Video transcript */
.transcript{
  border-left: 3px solid #eee;
  padding: 1rem;
  background: #fff;
  max-height: 45vh;
  overflow: auto;
  box-shadow: 0 1px 0 rgba(0,0,0,0.02);
  border-radius: 12px;
}
.transcript-inner p{
  margin-bottom: 0.75rem;
  color: #111;
  line-height: 1.55;
}

/* Resources list */
.resource-list{
  list-style: none;
  padding-left: 0;
  color: var(--muted);
}
.resource-list li{
  padding: 0.75rem 0;
  border-bottom: 1px dashed #eee;
}
.resource-list a{
  color: var(--accent);
  text-decoration: none;
  margin-left: 0.35rem;
}

/* Callout (System Modeler) */
.callout{
  background: #fff;
  border: 1px solid rgba(0,0,0,0.06);
  border-radius: 14px;
  padding: 1rem;
}
.callout-title{
  font-size: 0.9rem;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
  margin-bottom: 0.5rem;
}
.callout-text{
  color: #222;
  line-height: 1.55;
}

/* Author photo */
.author-photo{
  width: 120px;
  height: 120px;
  border-radius: 999px;
  object-fit: cover;
  border: 1px solid rgba(0,0,0,0.08);
  background: #fff;
}

/* Buttons */
.btn-primary{
  background: var(--accent);
  border-color: var(--accent);
}
.btn-outline-primary{
  color: var(--accent);
  border-color: rgba(42,111,151,0.25);
}
footer a{
  color: var(--accent);
  text-decoration: none;
}

/* Utility */
.visually-hidden{
  display: none !important;
}

@media (max-width: 576px){
  .display-4{ font-size: 1.8rem; }
  .lead{ font-size: 1rem; }
  .book-cover{ max-width: 280px; }
}