@import url('https://fonts.googleapis.com/css2?family=Shippori+Mincho:wght@500;700&family=Noto+Sans+JP:wght@400;500;700&family=Yomogi&family=JetBrains+Mono:wght@400;600&display=swap');

:root{
  --paper: #FAF6EC;
  --paper-deep: #F3EDDD;
  --rule: #DCD3BE;
  --margin: #E3B3A6;
  --ink: #24272B;
  --ink-soft: #55534d;
  --navy: #223A5E;
  --navy-soft: #3A5478;
  --akapen: #C1432A;
  --akapen-soft: #F6DCD3;
  --midori: #3F7355;
  --midori-soft: #DCE9DE;
  --gold: #B9871F;
  --shadow: rgba(36, 39, 43, 0.12);
  --radius: 3px;
  --sidebar-w: 280px;
}

*{ box-sizing: border-box; }

html{ scroll-behavior: smooth; }

body{
  margin:0;
  background: var(--paper);
  color: var(--ink);
  font-family: 'Noto Sans JP', sans-serif;
  line-height: 1.85;
  font-size: 16px;
}

/* --- notebook paper texture: faint horizontal rules + red margin line --- */
.page{
  position: relative;
  background-image:
    linear-gradient(var(--rule) 1px, transparent 1px);
  background-size: 100% 2.15em;
  background-position: 0 6.2em;
}
.page::before{
  content:"";
  position: absolute;
  top:0; bottom:0;
  left: 64px;
  width: 1px;
  background: var(--margin);
  opacity: .55;
  z-index: 0;
}
@media (max-width: 720px){
  .page::before{ left: 28px; }
}

a{ color: inherit; }

/* ---------------- bilingual toggle ---------------- */
.i18n-en{ display:none; }
body.lang-en .i18n-en{ display:inline; }
body.lang-en .i18n-ja{ display:none; }

.langsw{
  display:inline-flex;
  border: 1px solid #4a628a;
  border-radius: 20px;
  overflow:hidden;
  flex-shrink:0;
}
.langsw button{
  border:none;
  background: transparent;
  color:#B9C6DC;
  font-family:'JetBrains Mono',monospace;
  font-size: 11px;
  letter-spacing:.05em;
  padding: 5px 12px;
  cursor:pointer;
}
.langsw button.active{
  background: var(--akapen);
  color:#fff;
}
.sidebar .langsw button{ color:#B9C6DC; }
.topbar .langsw button{ color:#cfd8e8; font-size:10.5px; padding:4px 9px; }
.topbar .langsw{ border-color:#5a72988a; }

.eyebrow{
  font-family:'JetBrains Mono', monospace;
  font-size: 11px;
  letter-spacing: .14em;
  text-transform: uppercase;
  color: var(--navy-soft);
}

h1,h2,h3{
  font-family:'Shippori Mincho', serif;
  font-weight: 700;
  color: var(--navy);
  margin: 0 0 .4em;
}

/* ---------------- layout shell ---------------- */
.shell{
  display:flex;
  min-height: 100vh;
}

.sidebar{
  width: var(--sidebar-w);
  flex-shrink: 0;
  background: var(--navy);
  color: #EFE9DA;
  padding: 28px 22px 60px;
  position: sticky;
  top:0;
  height: 100vh;
  overflow-y:auto;
}
.sidebar::-webkit-scrollbar{ width:6px; }
.sidebar::-webkit-scrollbar-thumb{ background:#3d557c; border-radius:4px; }

.brand-row{
  display:flex;
  align-items:flex-start;
  justify-content:space-between;
  gap: 10px;
}
.brand{
  display:block;
  font-family:'Shippori Mincho', serif;
  font-size: 22px;
  font-weight: 700;
  color: #fff;
  text-decoration:none;
  margin-bottom: 4px;
}
.brand small{
  display:block;
  font-family:'Noto Sans JP',sans-serif;
  font-size: 11px;
  font-weight: 400;
  letter-spacing: .03em;
  color: #A9BAD3;
  margin-top: 4px;
}

.side-group{ margin-top: 28px; }
.side-group h4{
  font-family:'JetBrains Mono', monospace;
  font-size: 10.5px;
  letter-spacing: .12em;
  text-transform: uppercase;
  color: #90A3C2;
  margin: 0 0 10px;
  padding-bottom: 6px;
  border-bottom: 1px dashed #3d557c;
}
.side-group ul{ list-style:none; margin:0; padding:0; }
.side-group li{ margin: 1px 0; }
.side-group a{
  display:flex;
  gap:8px;
  align-items:baseline;
  text-decoration:none;
  color:#D7DEEC;
  font-size: 13.5px;
  padding: 6px 8px;
  border-radius: var(--radius);
  transition: background .15s, color .15s;
}
.side-group a .num{
  font-family:'JetBrains Mono',monospace;
  font-size: 10.5px;
  color:#7387AA;
  flex-shrink:0;
}
.side-group a:hover{ background:#2d4468; color:#fff; }
.side-group a.active{ background: var(--akapen); color:#fff; }
.side-group a.active .num{ color:#F6DCD3; }

.main{
  flex: 1;
  min-width: 0;
}

.topbar{
  display:none;
  align-items:center;
  justify-content:space-between;
  background: var(--navy);
  color:#fff;
  padding: 14px 18px;
  position: sticky; top:0; z-index: 30;
}
.topbar .brand{ font-size:18px; margin:0; }
.topbar-right{ display:flex; align-items:center; gap:10px; }
.topbar-right button[data-nav-toggle]{
  background:none;border:1px solid #4a628a;color:#fff;
  border-radius:4px; padding:6px 10px; font-size:13px;
}
@media (max-width: 900px){
  .shell{ flex-direction: column; }
  .sidebar{
    display: none;
    position: static;
    width: 100%;
    height: auto;
    max-height: 72vh;
    overflow-y: auto;
    box-shadow: 0 10px 24px rgba(0,0,0,.25);
  }
  .sidebar.open{ display: block; }
  .topbar{ display:flex; }
}

/* ---------------- hero (index) ---------------- */
.hero{
  padding: 74px 64px 50px;
  position: relative;
  z-index:1;
}
@media (max-width:720px){ .hero{ padding: 40px 28px 30px; } }

.hero .eyebrow{ margin-bottom: 14px; }
.hero h1{
  font-size: clamp(32px, 5vw, 52px);
  line-height:1.3;
  max-width: 15ch;
}
.hero h1 .ul{
  text-decoration: underline wavy var(--akapen);
  text-decoration-thickness: 2px;
  text-underline-offset: 6px;
}
.hero p.lead{
  max-width: 56ch;
  color: var(--ink-soft);
  font-size: 16.5px;
}
.hero .stamp{
  display:inline-block;
  margin-top: 22px;
  font-family:'Yomogi', cursive;
  color: var(--akapen);
  font-size: 20px;
  border: 2.5px solid var(--akapen);
  border-radius: 8px;
  padding: 6px 16px;
  transform: rotate(-3deg);
  opacity:.9;
}

.section-title{
  padding: 6px 64px;
  margin-top: 18px;
  display:flex;
  align-items:baseline;
  gap: 12px;
  position:relative; z-index:1;
}
@media (max-width:720px){ .section-title{ padding: 6px 28px; } }
.section-title h2{ font-size: 21px; margin:0; }
.section-title span{
  font-family:'JetBrains Mono',monospace;
  font-size:11px; color: var(--ink-soft); opacity:.7;
}

.grid{
  display:grid;
  grid-template-columns: repeat(auto-fill, minmax(240px,1fr));
  gap: 16px;
  padding: 18px 64px 60px;
  position:relative; z-index:1;
}
@media (max-width:720px){ .grid{ padding: 18px 28px 44px; grid-template-columns: 1fr 1fr;} }
@media (max-width:480px){ .grid{ grid-template-columns: 1fr; } }

.card{
  background: #fff;
  border: 1px solid var(--rule);
  border-left: 4px solid var(--navy);
  border-radius: var(--radius);
  padding: 16px 18px;
  text-decoration:none;
  color: var(--ink);
  display:block;
  box-shadow: 0 2px 0 var(--shadow);
  transition: transform .12s ease, box-shadow .12s ease, border-color .12s ease;
}
.card:hover{
  transform: translateY(-2px);
  box-shadow: 0 8px 18px var(--shadow);
  border-left-color: var(--akapen);
}
.card .num{
  font-family:'JetBrains Mono',monospace;
  font-size: 11px;
  color: var(--gold);
}
.card h3{
  font-size: 16.5px;
  margin: 6px 0 4px;
}
.card p{
  margin:0;
  font-size: 13px;
  color: var(--ink-soft);
  line-height: 1.6;
}

.footer{
  padding: 30px 64px 60px;
  color: var(--ink-soft);
  font-size: 12.5px;
  position: relative; z-index: 1;
}
@media (max-width:720px){ .footer{ padding: 20px 28px 40px; } }

/* ---------------- topic page ---------------- */
.topic-head{
  padding: 54px 64px 20px;
  position:relative; z-index:1;
}
@media (max-width:720px){ .topic-head{ padding:34px 28px 14px; } }

.crumb{
  font-family:'JetBrains Mono',monospace;
  font-size: 11.5px;
  color: var(--ink-soft);
  text-decoration:none;
  display:inline-flex;
  align-items:center;
  gap:6px;
  margin-bottom: 18px;
}
.crumb:hover{ color: var(--akapen); }

.tab{
  display:inline-block;
  background: var(--navy);
  color:#fff;
  font-family:'JetBrains Mono',monospace;
  font-size:12px;
  letter-spacing:.08em;
  padding: 4px 12px;
  border-radius: 3px 3px 0 0;
  margin-bottom: -1px;
}
.topic-head h1{
  font-size: clamp(26px,4vw,38px);
  border-top: 3px solid var(--navy);
  padding-top: 14px;
}
.topic-head .subtitle{
  font-size: 16px;
  color: var(--ink-soft);
  margin-top: -6px;
}

.content{
  padding: 10px 64px 30px;
  max-width: 780px;
  position:relative; z-index:1;
}
@media (max-width:720px){ .content{ padding: 10px 28px 20px; } }

.content p{ margin: 0 0 1.1em; }

.block{ margin: 34px 0; }
.block > h2{
  font-size: 19px;
  display:flex; align-items:center; gap:10px;
}
.block > h2 .marker{
  width:9px;height:9px;border-radius:50%;
  background: var(--akapen);
  display:inline-block;
}

.formbox{
  background: var(--paper-deep);
  border: 1px dashed var(--navy-soft);
  border-radius: 6px;
  padding: 16px 20px;
  font-family:'JetBrains Mono', monospace;
  font-size: 14.5px;
  color: var(--navy);
  margin: 10px 0 6px;
}
.formbox .note{
  display:block;
  margin-top:8px;
  font-family:'Noto Sans JP',sans-serif;
  font-size: 13px;
  color: var(--ink-soft);
}

.example{
  background:#fff;
  border:1px solid var(--rule);
  border-radius: var(--radius);
  padding: 16px 20px;
  margin: 14px 0;
  box-shadow: 0 1px 0 var(--shadow);
}
.example .en{
  font-family:'JetBrains Mono', monospace;
  font-size: 16px;
  color: var(--ink);
}
.example mark{
  background: none;
  color: var(--navy);
  font-weight: 600;
  text-decoration: underline wavy var(--akapen);
  text-decoration-thickness: 2px;
  text-underline-offset: 4px;
}
.example .ja{
  font-family:'Yomogi', cursive;
  color: var(--akapen);
  font-size: 17px;
  margin-top: 8px;
  padding-left: 2px;
}
.example .note{
  font-size: 12.5px;
  color: var(--ink-soft);
  margin-top: 6px;
  border-top: 1px dotted var(--rule);
  padding-top: 6px;
}

.points{
  list-style: none;
  margin: 10px 0 0;
  padding: 0;
}
.points li{
  position: relative;
  padding: 8px 8px 8px 30px;
  background: var(--midori-soft);
  border-radius: var(--radius);
  margin-bottom: 8px;
  font-size: 14.5px;
  color: #234a34;
}
.points li::before{
  content:"✓";
  position:absolute; left:9px; top:7px;
  color: var(--midori);
  font-weight:700;
}

.mistake{
  background: var(--akapen-soft);
  border-left: 4px solid var(--akapen);
  border-radius: var(--radius);
  padding: 12px 16px;
  font-size: 14px;
  color: #6b2415;
  margin-top: 14px;
}
.mistake strong{ color: var(--akapen); }

.pager{
  display:flex;
  justify-content: space-between;
  gap: 12px;
  padding: 30px 64px 60px;
  max-width: 780px;
  position:relative; z-index:1;
}
@media (max-width:720px){ .pager{ padding: 20px 28px 40px; } }
.pager a{
  flex:1;
  text-decoration:none;
  border: 1px solid var(--rule);
  border-radius: var(--radius);
  padding: 12px 16px;
  background:#fff;
  font-size: 13.5px;
  color: var(--ink-soft);
}
.pager a .lbl{
  display:block;
  font-family:'JetBrains Mono',monospace;
  font-size: 10.5px;
  color: var(--gold);
  margin-bottom: 4px;
}
.pager a:hover{ border-color: var(--akapen); color: var(--ink); }
.pager a.next{ text-align:right; }

/* ---- 拡充版ページ用（例文グループ・早見表・確認クイズ） ---- */
.ex-group{
  font-size: 15px;
  margin: 28px 0 4px;
  padding-bottom: 5px;
  border-bottom: 1px solid var(--rule);
  color: var(--navy);
}
.gtable{
  width:100%;
  border-collapse: collapse;
  background:#fff;
  margin: 12px 0 8px;
  font-size: 14.5px;
}
.gtable th, .gtable td{
  border: 1px solid var(--rule);
  padding: 8px 12px;
  text-align: left;
}
.gtable th{ background: var(--paper-deep); color: var(--navy); font-weight: 700; }
.gtable td.en{ font-family:'JetBrains Mono', monospace; }
.quiz{ list-style: none; margin: 10px 0 0; padding: 0; counter-reset: q; }
.quiz li{
  counter-increment: q;
  background:#fff;
  border:1px solid var(--rule);
  border-radius: var(--radius);
  padding: 12px 16px 12px 44px;
  margin-bottom: 10px;
  position: relative;
}
.quiz li::before{
  content: counter(q);
  position:absolute; left:14px; top:12px;
  width:22px; height:22px; border-radius:50%;
  background: var(--navy); color:#fff; font-size:12px; font-weight:700;
  display:flex; align-items:center; justify-content:center;
}
.quiz .q{ font-family:'JetBrains Mono', monospace; font-size: 15.5px; }
.quiz details{ margin-top: 8px; }
.quiz summary{ cursor:pointer; font-size: 13px; color: var(--midori); font-weight:700; }
.quiz .a{ margin-top:6px; font-size:14px; color: var(--ink); }
.quiz .a b{ color: var(--akapen); font-family:'JetBrains Mono', monospace; }
.mistake + .mistake{ margin-top: 10px; }