:root {
  --ys-purple: rgb(78,28,197);
  --ys-gold: #C39000;
  --text: #333333;
  --muted: #666666;
  --bg: #ffffff;
}

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Hiragino Kaku Gothic ProN", "Noto Sans JP", "Yu Gothic", "Meiryo", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  /* line-height: 1.85; */
  font-size: 16px;
}

.container {
  max-width: 860px;
  padding: 0 24px;
  margin: 72px auto 120px;
}

.page-header { margin-bottom: 32px; }
.page-title {
  margin: 0 0 6px;
  color: var(--ys-purple);
  font-weight: 800;
  font-size: clamp(22px, 2.6vw, 28px);
}
.page-subtitle {
  margin: 0;
  color: var(--ys-gold);
  font-weight: 700;
  font-size: 13px;
  letter-spacing: .02em;
}

.lead p { color: #444; }

.article { margin-top: 36px; }
.article-title {
  margin: 0 0 12px;
  padding-bottom: 10px;
  font-size: clamp(18px, 2.2vw, 20px);
  font-weight: 800;
  color: #222;
  /* 二重ライン風のアンダーライン */
  border-bottom: 1px solid #444;
  position: relative;
}
.article-title::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -2px;
  width: 180px;
  height: 3px;
  background: var(--ys-purple);
}

.article-list {
  margin: 0;
  padding-left: 1.4em;
}
.article-list li { margin: .5em 0; }

.updated {
  margin-top: 40px;
  color: var(--muted);
  font-size: 0.95em;
}

ページトップボタン
.back-to-top {
  position: fixed;
  right: 20px;
  bottom: 20px;
  width: 44px;
  height: 44px;
  display: grid;
  place-items: center;
  color: var(--ys-purple);
  background: #fff;
  border: 1px solid #eee;
  border-radius: 50%;
  text-decoration: none;
  box-shadow: 0 4px 14px rgba(0,0,0,.08);
  opacity: 0;
  pointer-events: none;
  transition: opacity .25s ease, transform .25s ease, box-shadow .25s ease;
}
.back-to-top.is-visible {
  opacity: 1;
  pointer-events: auto;
}
.back-to-top:hover { box-shadow: 0 6px 18px rgba(0,0,0,.12); transform: translateY(-2px); }

@media (max-width: 640px){
  .container { margin: 56px auto 100px; }
  .article-title::after { width: 140px; }
}