@import url('https://fonts.googleapis.com/css2?family=Noto+Serif+JP:wght@400;600&family=Noto+Sans+JP:wght@300;400;500&display=swap');

:root {
  --green-deep:   #1e4d35;
  --green-mid:    #2d6a4f;
  --green-light:  #52b788;
  --green-pale:   #d8f3dc;
  --green-bg:     #f2f7f4;
  --text-primary: #1a1a1a;
  --text-muted:   #6b7b72;
  --border:       #d0e4d8;
  --white:        #ffffff;
}

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

body {
  font-family: "Noto Sans JP", "Hiragino Kaku Gothic ProN", sans-serif;
  font-weight: 400;
  background: var(--green-bg);
  color: var(--text-primary);
  line-height: 1.9;
  -webkit-font-smoothing: antialiased;
}

/* ── Header ── */
header {
  background: var(--green-deep);
  color: var(--white);
  padding: 3rem 2rem 2.5rem;
  position: relative;
  overflow: hidden;
}

header::after {
  content: '';
  position: absolute;
  bottom: 0; left: 0; right: 0;
  height: 3px;
  background: linear-gradient(90deg, var(--green-light), transparent);
}

.header-inner {
  max-width: 920px;
  margin: 0 auto;
}

header h1 {
  font-family: "Noto Serif JP", serif;
  font-size: 1.75rem;
  font-weight: 600;
  letter-spacing: 0.12em;
  line-height: 1.4;
}

.subtitle {
  font-size: 0.82rem;
  font-weight: 300;
  letter-spacing: 0.22em;
  color: var(--green-pale);
  margin-top: 0.5rem;
  text-transform: uppercase;
}

/* ── Tab Nav ── */
.tab-nav {
  background: var(--white);
  border-bottom: 1px solid var(--border);
  display: flex;
  padding: 0 calc((100% - 920px) / 2);
}

.tab-btn {
  background: none;
  border: none;
  padding: 1.1rem 2rem;
  font-size: 1rem;
  font-family: "Noto Sans JP", sans-serif;
  font-weight: 400;
  letter-spacing: 0.1em;
  cursor: pointer;
  color: var(--text-muted);
  border-bottom: 2px solid transparent;
  margin-bottom: -1px;
  transition: color 0.2s, border-color 0.2s;
}

.tab-btn:hover {
  color: var(--green-mid);
}

.tab-btn.active {
  color: var(--green-deep);
  border-bottom-color: var(--green-light);
  font-weight: 500;
}

/* ── Main ── */
main {
  max-width: 920px;
  margin: 0 auto;
  padding: 2.5rem 2rem 5rem;
}

.tab-content {
  display: none;
}

.tab-content.active {
  display: block;
}

.tab-content > h2 {
  font-family: "Noto Serif JP", serif;
  font-size: 1.25rem;
  font-weight: 600;
  color: var(--green-deep);
  letter-spacing: 0.15em;
  margin-bottom: 2rem;
  padding-bottom: 0.75rem;
  border-bottom: 1px solid var(--border);
}

/* ── Year / Month ── */
.year-section {
  margin-bottom: 3rem;
}

.year-section > h3 {
  font-family: "Noto Serif JP", serif;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--white);
  background: var(--green-mid);
  display: inline-block;
  padding: 0.3rem 1.1rem;
  border-radius: 2px;
  letter-spacing: 0.12em;
  margin-bottom: 1.25rem;
}

.month-section {
  display: grid;
  grid-template-columns: 4rem 1fr;
  gap: 0 1.5rem;
  margin-bottom: 1.4rem;
  align-items: start;
}

.month-section > h4 {
  font-size: 0.9rem;
  font-weight: 500;
  color: var(--green-mid);
  letter-spacing: 0.08em;
  padding-top: 0.35rem;
  text-align: right;
  white-space: nowrap;
}

.month-section > ul {
  list-style: none;
  border-left: 1px solid var(--border);
  padding-left: 1.25rem;
}

.month-section ul li {
  font-size: 1rem;
  font-weight: 400;
  padding: 0.35rem 0;
  color: var(--text-primary);
  position: relative;
}

.month-section ul li::before {
  content: '';
  position: absolute;
  left: -1.32rem;
  top: 0.75rem;
  width: 5px;
  height: 5px;
  border-radius: 50%;
  background: var(--green-light);
}

.month-section ul li a {
  color: var(--green-mid);
  text-decoration: none;
  border-bottom: 1px solid var(--green-pale);
  transition: border-color 0.15s, color 0.15s;
}

.month-section ul li a:hover {
  color: var(--green-deep);
  border-bottom-color: var(--green-light);
}

/* ── Seminars ── */
.seminars-intro {
  font-size: 1rem;
  color: var(--text-muted);
  margin-bottom: 2rem;
}

.seminars-list {
  display: grid;
  gap: 1px;
  background: var(--border);
  border: 1px solid var(--border);
  border-radius: 6px;
  overflow: hidden;
}

.seminar-card {
  background: var(--white);
  padding: 1.5rem 1.75rem;
  transition: background 0.15s;
}

.seminar-card:hover {
  background: #f8fbf9;
}

.seminar-card h3 {
  font-family: "Noto Serif JP", serif;
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--green-deep);
  margin-bottom: 0.35rem;
  letter-spacing: 0.05em;
}

.seminar-card .seminar-meta {
  font-size: 0.9rem;
  color: var(--text-muted);
  letter-spacing: 0.05em;
  margin-bottom: 0.6rem;
}

.seminar-card p {
  font-size: 0.98rem;
  color: var(--text-primary);
  margin-bottom: 0.75rem;
  line-height: 1.8;
}

.seminar-card .seminar-links {
  display: flex;
  gap: 1.5rem;
}

.seminar-card .seminar-links a {
  font-size: 0.93rem;
  color: var(--green-mid);
  text-decoration: none;
  border-bottom: 1px solid var(--green-pale);
  letter-spacing: 0.03em;
  transition: border-color 0.15s, color 0.15s;
}

.seminar-card .seminar-links a:hover {
  color: var(--green-deep);
  border-bottom-color: var(--green-light);
}

/* ── Footer ── */
footer {
  background: var(--green-deep);
  color: rgba(255,255,255,0.45);
  text-align: center;
  padding: 1.75rem;
  font-size: 0.75rem;
  letter-spacing: 0.1em;
}

/* ── Responsive ── */
@media (max-width: 640px) {
  header { padding: 2rem 1.25rem 1.75rem; }
  header h1 { font-size: 1.3rem; }
  .tab-nav { padding: 0 0.5rem; }
  .tab-btn { padding: 1rem 1.25rem; font-size: 0.85rem; }
  main { padding: 2rem 1.25rem 4rem; }

  .month-section {
    grid-template-columns: 2.5rem 1fr;
    gap: 0 1rem;
  }
}