/* ============================================================
   CIVILINE — Civil Engineering NPTEL Knowledge Hub
   Design concept: "Working Blueprint" — deep blueprint blue,
   drafting grid, dimension lines, corner registration marks.
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=IBM+Plex+Mono:wght@400;500;600;700&family=IBM+Plex+Sans:wght@400;500;600;700;800&display=swap');

:root{
  --blueprint:#0A3D62;
  --blueprint-deep:#082C47;
  --linework:#7FD1FF;
  --paper:#EDEFF2;
  --paper-dim:#C9D2DA;
  --ink:#12181D;
  --signal:#F2A93C;
  --safety-red:#C1442D;
  --ok-green:#4C9A6A;
  --radius:4px;
}

*{margin:0;padding:0;box-sizing:border-box;}
html{scroll-behavior:smooth;}
body{
  background:var(--blueprint);
  color:var(--paper);
  font-family:'IBM Plex Sans',sans-serif;
  background-image:
    linear-gradient(var(--linework) 1px, transparent 1px),
    linear-gradient(90deg, var(--linework) 1px, transparent 1px);
  background-size:42px 42px;
  background-attachment:fixed;
  position:relative;
}
body::before{
  content:"";
  position:fixed;
  inset:0;
  background:linear-gradient(var(--blueprint) 0%, var(--blueprint) 100%);
  opacity:0.94;
  z-index:-1;
}
a{color:inherit;text-decoration:none;}
.mono{font-family:'IBM Plex Mono',monospace;}

/* corner registration marks, used on hero + section frames */
.tick-frame{position:relative;}
.tick-frame::before,.tick-frame::after,
.tick-frame .tick-br,.tick-frame .tick-bl{
  content:"";
  position:absolute;
  width:18px;height:18px;
  border-color:var(--linework);
  opacity:0.7;
}
.tick-frame::before{top:0;left:0;border-top:2px solid;border-left:2px solid;}
.tick-frame::after{top:0;right:0;border-top:2px solid;border-right:2px solid;}
.tick-frame .tick-bl{bottom:0;left:0;border-bottom:2px solid var(--linework);border-left:2px solid var(--linework);}
.tick-frame .tick-br{bottom:0;right:0;border-bottom:2px solid var(--linework);border-right:2px solid var(--linework);}

/* ---------- NAV ---------- */
nav{
  display:flex;
  justify-content:space-between;
  align-items:center;
  padding:22px 6vw;
  border-bottom:1px solid rgba(127,209,255,0.25);
  background:rgba(8,44,71,0.55);
  backdrop-filter:blur(6px);
  position:sticky;
  top:0;
  z-index:50;
}
.logo{
  font-family:'IBM Plex Mono',monospace;
  font-weight:700;
  font-size:1.15rem;
  letter-spacing:0.04em;
  display:flex;
  align-items:center;
  gap:10px;
}
.logo .mark{
  width:28px;height:28px;
  border:2px solid var(--signal);
  display:flex;align-items:center;justify-content:center;
  font-size:0.75rem;
  color:var(--signal);
  transform:rotate(45deg);
}
.logo .mark span{transform:rotate(-45deg);}
.nav-links{display:flex;gap:30px;font-size:0.82rem;text-transform:uppercase;letter-spacing:0.08em;font-weight:600;}
.nav-links a{opacity:0.75;transition:opacity 0.2s,color 0.2s;}
.nav-links a:hover{opacity:1;color:var(--linework);}

/* ---------- HERO ---------- */
.hero{
  padding:9vh 6vw 7vh;
  max-width:1200px;
  margin:0 auto;
}
.eyebrow{
  display:inline-flex;
  align-items:center;
  gap:10px;
  font-family:'IBM Plex Mono',monospace;
  font-size:0.72rem;
  letter-spacing:0.12em;
  text-transform:uppercase;
  color:var(--linework);
  border:1px solid rgba(127,209,255,0.4);
  padding:6px 14px;
  border-radius:999px;
  margin-bottom:28px;
}
.eyebrow::before{content:"§";color:var(--signal);}
.hero h1{
  font-size:clamp(2.4rem,6vw,4.6rem);
  font-weight:800;
  line-height:1.05;
  letter-spacing:-0.01em;
  max-width:820px;
}
.hero h1 .accent{color:var(--signal);}
.hero p{
  margin-top:24px;
  max-width:560px;
  color:var(--paper-dim);
  font-size:1.05rem;
  line-height:1.65;
}
.hero-stats{
  display:flex;
  gap:0;
  margin-top:48px;
  border-top:1px solid rgba(127,209,255,0.25);
  padding-top:20px;
  flex-wrap:wrap;
}
.stat{
  padding:0 32px 0 0;
  margin-right:32px;
  border-right:1px solid rgba(127,209,255,0.2);
}
.stat:last-child{border-right:none;}
.stat .num{font-family:'IBM Plex Mono',monospace;font-size:2rem;font-weight:700;color:var(--signal);}
.stat .label{font-size:0.78rem;color:var(--paper-dim);text-transform:uppercase;letter-spacing:0.06em;margin-top:4px;}

/* ---------- SECTION ---------- */
section{padding:6vh 6vw;max-width:1200px;margin:0 auto;}
.section-head{
  display:flex;
  justify-content:space-between;
  align-items:flex-end;
  margin-bottom:36px;
  flex-wrap:wrap;
  gap:14px;
  border-bottom:1px dashed rgba(127,209,255,0.3);
  padding-bottom:18px;
}
.section-head .tag{
  font-family:'IBM Plex Mono',monospace;
  font-size:0.75rem;
  color:var(--linework);
  text-transform:uppercase;
  letter-spacing:0.1em;
  margin-bottom:8px;
}
.section-head h2{font-size:clamp(1.8rem,4vw,2.6rem);font-weight:800;}
.section-head p{color:var(--paper-dim);max-width:360px;font-size:0.92rem;}

/* ---------- SUBJECT GRID ---------- */
.subject-grid{
  display:grid;
  grid-template-columns:repeat(auto-fit,minmax(270px,1fr));
  gap:20px;
}
.subject-card{
  background:rgba(237,239,242,0.04);
  border:1px solid rgba(127,209,255,0.25);
  border-radius:var(--radius);
  padding:26px;
  position:relative;
  transition:transform 0.18s,border-color 0.18s,background 0.18s;
  display:flex;
  flex-direction:column;
  min-height:230px;
}
.subject-card:hover{
  transform:translateY(-4px);
  border-color:var(--signal);
  background:rgba(237,239,242,0.07);
}
.subject-card .idx{
  font-family:'IBM Plex Mono',monospace;
  font-size:0.72rem;
  color:var(--signal);
  letter-spacing:0.08em;
  margin-bottom:14px;
}
.subject-card h3{font-size:1.35rem;font-weight:700;margin-bottom:10px;line-height:1.2;}
.subject-card p{color:var(--paper-dim);font-size:0.88rem;line-height:1.55;flex-grow:1;}
.subject-card .meta{
  display:flex;
  justify-content:space-between;
  align-items:center;
  margin-top:18px;
  padding-top:16px;
  border-top:1px solid rgba(127,209,255,0.15);
  font-family:'IBM Plex Mono',monospace;
  font-size:0.72rem;
  color:var(--linework);
  text-transform:uppercase;
  letter-spacing:0.05em;
}
.subject-card .arrow{transition:transform 0.18s;}
.subject-card:hover .arrow{transform:translateX(4px);}

/* ---------- BUTTONS ---------- */
.btn{
  display:inline-flex;
  align-items:center;
  gap:8px;
  padding:14px 26px;
  font-weight:700;
  font-size:0.85rem;
  text-transform:uppercase;
  letter-spacing:0.05em;
  border-radius:var(--radius);
  border:none;
  cursor:pointer;
  transition:transform 0.15s,opacity 0.15s;
}
.btn:hover{transform:translateY(-2px);}
.btn-primary{background:var(--signal);color:var(--ink);}
.btn-ghost{border:1px solid var(--linework);color:var(--linework);background:transparent;}
.btn-ghost:hover{background:rgba(127,209,255,0.1);}
.btn-block{width:100%;justify-content:center;}

/* ---------- SUBJECT PAGE ---------- */
.subject-header{
  padding:6vh 6vw 4vh;
  max-width:1000px;
  margin:0 auto;
}
.breadcrumb{
  font-family:'IBM Plex Mono',monospace;
  font-size:0.78rem;
  color:var(--linework);
  margin-bottom:24px;
}
.breadcrumb a{opacity:0.8;}
.breadcrumb a:hover{opacity:1;text-decoration:underline;}
.subject-header h1{font-size:clamp(2rem,5vw,3.2rem);font-weight:800;margin-bottom:16px;}
.subject-header .desc{color:var(--paper-dim);max-width:640px;line-height:1.65;font-size:1.02rem;}

.diagram-box{
  max-width:1000px;
  margin:0 auto 6vh;
  padding:0 6vw;
}
.diagram-frame{
  background:rgba(237,239,242,0.05);
  border:1px solid rgba(127,209,255,0.25);
  border-radius:var(--radius);
  padding:30px;
  display:flex;
  justify-content:center;
  position:relative;
}
.diagram-frame img{max-width:100%;height:auto;max-height:320px;}
.diagram-caption{
  text-align:center;
  color:var(--paper-dim);
  font-size:0.82rem;
  margin-top:12px;
  font-family:'IBM Plex Mono',monospace;
}

.lecture-box{
  max-width:1000px;
  margin:0 auto 6vh;
  padding:0 6vw;
}
.lecture-card{
  background:rgba(242,169,60,0.08);
  border:1px solid rgba(242,169,60,0.4);
  border-radius:var(--radius);
  padding:26px 30px;
  display:flex;
  justify-content:space-between;
  align-items:center;
  flex-wrap:wrap;
  gap:16px;
}
.lecture-card .info h3{font-size:1.1rem;margin-bottom:6px;}
.lecture-card .info p{color:var(--paper-dim);font-size:0.85rem;}

/* ---------- QUIZ ---------- */
.quiz-box{
  max-width:1000px;
  margin:0 auto 8vh;
  padding:0 6vw;
}
.quiz-progress{
  display:flex;
  justify-content:space-between;
  align-items:center;
  margin-bottom:24px;
  font-family:'IBM Plex Mono',monospace;
  font-size:0.8rem;
  color:var(--linework);
}
.progress-track{
  flex-grow:1;
  height:4px;
  background:rgba(127,209,255,0.15);
  margin:0 16px;
  border-radius:2px;
  overflow:hidden;
}
.progress-fill{
  height:100%;
  background:var(--signal);
  width:0%;
  transition:width 0.3s;
}
.question-card{
  background:rgba(237,239,242,0.04);
  border:1px solid rgba(127,209,255,0.2);
  border-radius:var(--radius);
  padding:28px;
  margin-bottom:18px;
}
.question-card .qnum{
  font-family:'IBM Plex Mono',monospace;
  font-size:0.75rem;
  color:var(--signal);
  margin-bottom:10px;
  letter-spacing:0.05em;
}
.question-card .qtext{font-size:1.08rem;font-weight:600;margin-bottom:20px;line-height:1.5;}
.options{display:flex;flex-direction:column;gap:10px;}
.option{
  display:flex;
  align-items:center;
  gap:12px;
  padding:13px 16px;
  border:1px solid rgba(127,209,255,0.25);
  border-radius:var(--radius);
  cursor:pointer;
  transition:border-color 0.15s,background 0.15s;
  font-size:0.94rem;
}
.option:hover{border-color:var(--linework);background:rgba(127,209,255,0.06);}
.option.selected{border-color:var(--linework);background:rgba(127,209,255,0.1);}
.option.correct{border-color:var(--ok-green);background:rgba(76,154,106,0.18);}
.option.incorrect{border-color:var(--safety-red);background:rgba(193,68,45,0.18);}
.option .letter{
  font-family:'IBM Plex Mono',monospace;
  font-weight:700;
  color:var(--linework);
  min-width:20px;
}
.explanation{
  margin-top:16px;
  padding:14px 16px;
  background:rgba(127,209,255,0.06);
  border-left:3px solid var(--linework);
  font-size:0.86rem;
  color:var(--paper-dim);
  line-height:1.55;
  display:none;
}
.explanation.show{display:block;}

.quiz-footer{
  display:flex;
  justify-content:space-between;
  align-items:center;
  margin-top:30px;
  flex-wrap:wrap;
  gap:16px;
}
.score-display{
  font-family:'IBM Plex Mono',monospace;
  font-size:1rem;
  color:var(--signal);
  font-weight:700;
}

/* ---------- FOOTER ---------- */
footer{
  padding:5vh 6vw;
  border-top:1px solid rgba(127,209,255,0.2);
  display:flex;
  justify-content:space-between;
  align-items:center;
  color:var(--paper-dim);
  font-size:0.82rem;
  flex-wrap:wrap;
  gap:12px;
  font-family:'IBM Plex Mono',monospace;
}

@media (max-width:700px){
  .nav-links{display:none;}
  .lecture-card{flex-direction:column;align-items:flex-start;}
}

@media (prefers-reduced-motion:reduce){
  *{transition:none !important;}
}