html, body {
  margin: 0;
  padding: 0;
  background-color: #ffffff;
  font-family: 'Times New Roman', Times, serif;
}

/* Header Banner */
.header-banner {
  background-color: #551d75;
  color: #ffffff;
  padding: 25px 40px;
}

.header-content {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: relative;
}

.title-group {
  text-align: center;
  flex-grow: 1;
}

.main-title {
  font-size: 3.6rem;
  font-weight: bold;
  margin: 0;
}

.subtitle {
  font-size: 1.8rem;
  margin: 5px 0 0 0;
  font-weight: normal;
}

/* Header Navigation Links */
header a,
header a:link,
header a:visited,
.nav-unit-link,
.nav-unit-link:link,
.nav-unit-link:visited {
  color: #ffffff !important;
  text-decoration: none !important;
  display: flex;
  align-items: center;
  gap: 12px;
  font-size: 1.5rem;
  font-weight: bold;
  position: absolute;
  transition: transform 0.2s ease, opacity 0.2s ease;
}

.prev-unit-link {
  left: 0;
}

/* Hover Shift Left for Previous Unit */
.prev-unit-link:hover {
  transform: translateX(-6px);
  opacity: 0.9;
}

.next-unit-link {
  right: 0;
}

/* Hover Shift Right for Next Unit */
.next-unit-link:hover {
  transform: translateX(6px);
  opacity: 0.9;
}

.arrow {
  font-size: 2.2rem;
  line-height: 1;
}

/* Layout Wrapper */
.wrapper {
  max-width: 950px;
  margin: 0 auto;
  padding: 30px 20px;
}

.back-link,
.back-link:link {
  display: inline-block;
  margin-bottom: 35px;
  color: #005b94;
  text-decoration: underline;
  font-weight: bold;
  font-size: 1.1rem;
}

.back-link:visited {
  color: #551a8b;
}

/* Topic Rows */
.topics-list {
  display: flex;
  flex-direction: column;
  gap: 16px;
  margin-bottom: 60px;
}

.topic-row {
  display: flex;
  align-items: baseline;
  gap: 35px;
}

.topic-number {
  font-size: 1.6rem;
  font-weight: bold;
  min-width: 140px;
}

.topic-title {
  font-size: 1.5rem;
}

/* Standard Body Links (Blue Unclicked, Purple Visited) */
.topic-number a:link,
.topic-title a:link,
.summary-title a:link {
  color: #0000ee;
  text-decoration: underline;
}

.topic-number a:visited,
.topic-title a:visited,
.summary-title a:visited {
  color: #551a8b;
  text-decoration: underline;
}

/* Unit Summary Header */
.summary-section {
  text-align: center;
  margin-top: 40px;
}

.summary-title {
  font-size: 2.5rem;
  font-weight: bold;
  margin-bottom: 20px;
}