/* ─── CONTEXT STRIP (for non-teacher visitors) ──────────────── */
.context-strip {
  min-height: auto;
  background: var(--bg1);
  padding: clamp(40px, 7vh, 64px) var(--gut);
  border-top: 1px solid var(--card-border);
  border-bottom: 1px solid var(--card-border);
  position: relative; z-index: 5;
}
.context-strip::before {
  content: '';
  position: absolute; inset: 0;
  background:
    radial-gradient(ellipse 60% 80% at 50% 50%, rgba(21,89,163,0.07) 0%, transparent 100%);
  pointer-events: none;
}
.context-strip > * { position: relative; z-index: 1; }

.context-intro {
  font-family: var(--mono);
  font-size: 11px; letter-spacing: 0.26em; text-transform: uppercase;
  color: var(--txt2); margin-bottom: 24px;
}
.context-intro::before { content: '[ '; color: var(--blue-lt); }
.context-intro::after  { content: ' ]'; color: var(--blue-lt); }

.context-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1px;
  background: var(--card-border);
}
@media (min-width: 700px) {
  .context-grid { grid-template-columns: 1fr 1fr 1fr; }
}

.context-card {
  background: var(--bg1);
  padding: clamp(20px, 3vw, 32px);
  position: relative;
}
.context-card::before {
  content: '';
  position: absolute; top: 0; left: 0; right: 0; height: 2px;
}
.context-card:nth-child(1)::before { background: var(--ga); }
.context-card:nth-child(2)::before { background: var(--gb); }
.context-card:nth-child(3)::before { background: var(--gc); }

.ctx-stat {
  font-family: var(--sans);
  font-size: clamp(36px, 5vw, 52px);
  font-weight: 900; line-height: 1;
  letter-spacing: -0.02em;
}
.context-card:nth-child(1) .ctx-stat { color: var(--red-lt); }
.context-card:nth-child(2) .ctx-stat { color: var(--blue-lt); }
.context-card:nth-child(3) .ctx-stat { color: var(--green-lt); }

.ctx-label {
  font-family: var(--mono); font-size: 11px;
  letter-spacing: 0.22em; text-transform: uppercase;
  color: var(--txt2); margin-top: 8px;
}
.ctx-desc {
  font-size: 14px; line-height: 1.55; color: var(--txt1); margin-top: 10px;
}
.ctx-desc strong { color: var(--txt0); font-weight: 600; }

/* ─── PROOF STRIP ───────────────────────────────────────────── */
.proof-strip {
  min-height: auto;
  background: var(--bg0);
  padding: clamp(56px, 9vh, 80px) var(--gut);
  position: relative; z-index: 5;
  border-bottom: 1px solid var(--card-border);
}
.proof-strip::before {
  content: '';
  position: absolute; inset: 0;
  background: radial-gradient(ellipse 80% 60% at 50% 50%, rgba(17,117,64,0.06) 0%, transparent 100%);
  pointer-events: none;
}
.proof-grid {
  display: grid; grid-template-columns: repeat(2,1fr); gap: 1px;
  background: var(--card-border); max-width: 900px;
  position: relative; z-index: 1;
}
@media (min-width: 700px) {
  .proof-grid { grid-template-columns: repeat(4,1fr); }
}
.proof-item {
  background: var(--bg0); padding: clamp(20px, 3vw, 32px) clamp(16px, 2vw, 24px);
  position: relative;
}
.proof-item::after {
  content: '';
  position: absolute; top: 0; left: 0; right: 0; height: 2px;
}
.proof-item:nth-child(1)::after { background: var(--ga); }
.proof-item:nth-child(2)::after { background: var(--gb); }
.proof-item:nth-child(3)::after { background: var(--gc); }
.proof-item:nth-child(4)::after { background: linear-gradient(90deg, var(--ga), var(--gc)); }

.proof-num {
  font-family: var(--sans); font-size: clamp(44px, 6vw, 64px);
  font-weight: 900; line-height: 1; letter-spacing: -0.02em;
}
.proof-item:nth-child(1) .proof-num { color: var(--red-lt); }
.proof-item:nth-child(2) .proof-num { color: var(--blue-lt); }
.proof-item:nth-child(3) .proof-num { color: var(--green-lt); }
.proof-item:nth-child(4) .proof-num { color: var(--txt0); }

.proof-unit { font-size: 0.42em; color: var(--txt2); font-weight: 700; margin-left: 2px; letter-spacing: 0; -webkit-text-fill-color: var(--txt2); }
.proof-label { font-family: var(--mono); font-size: 10px; letter-spacing: 0.2em; color: var(--txt2); text-transform: uppercase; margin-top: 10px; }
.proof-sub { font-size: 12px; color: var(--txt3); margin-top: 5px; line-height: 1.4; }

:root[data-theme="light"] .proof-strip { background: var(--bg0); }
:root[data-theme="light"] .proof-item { background: var(--bg0); }

/* ─── PROBLEM ───────────────────────────────────────────────── */
.problem { background: var(--bg1); }
.problem::before {
  content: '';
  position: absolute; inset: 0;
  background:
    radial-gradient(ellipse 50% 70% at 0% 50%, rgba(196,30,58,0.13) 0%, transparent 100%),
    url('/assets/molecule.jpg') no-repeat center center / cover;
  opacity: 0.10;
  mix-blend-mode: screen;
  z-index: 0; pointer-events: none;
}
:root[data-theme="light"] .problem::before { mix-blend-mode: multiply; opacity: 0.06; }

.prob-headline {
  font-family: var(--sans); font-weight: 900;
  line-height: 0.9; letter-spacing: -0.03em;
  text-transform: uppercase;
  font-size: clamp(48px, 10vw, 112px);
  margin-top: 18px; max-width: 13ch;
  position: relative; z-index: 1;
}
.prob-headline .r { color: var(--red-lt); }

.problem-grid {
  margin-top: clamp(28px, 5vh, 44px);
  display: grid; grid-template-columns: 1fr; gap: 12px;
  position: relative; z-index: 2;
}
@media (min-width: 700px) {
  .problem-grid { grid-template-columns: 1fr 1fr; gap: 14px; }
}
.prob-cell {
  background: var(--card-bg); border: 1px solid var(--card-border);
  padding: 24px;
  opacity: 0; transform: translateY(36px);
}
.prob-cell.r { background: linear-gradient(180deg, rgba(196,30,58,0.07) 0%, var(--card-bg) 60%); }
.prob-cell.b { background: linear-gradient(180deg, rgba(21,89,163,0.08) 0%, var(--card-bg) 60%); }
.prob-cell.g { background: linear-gradient(180deg, rgba(17,117,64,0.07) 0%, var(--card-bg) 60%); }
.prob-cell.d { background: linear-gradient(180deg, rgba(160,108,32,0.06) 0%, var(--card-bg) 60%); }
.prob-num { font-family: var(--sans); font-size: clamp(40px, 5vw, 56px); font-weight: 900; line-height: 1; letter-spacing: -0.02em; }
.prob-num .u { font-size: 0.38em; color: var(--txt2); font-weight: 700; margin-left: 3px; letter-spacing: 0; }
.prob-lbl { font-size: 14px; color: var(--txt1); margin-top: 12px; line-height: 1.45; }
.prob-lbl-mono { font-family: var(--mono); font-size: 10px; letter-spacing: 0.2em; color: var(--txt3); text-transform: uppercase; margin-top: 8px; }

/* ─── HOW IT WORKS ──────────────────────────────────────────── */
.how-sec {
  background: var(--bg0);
}
.how-sec::before {
  content: '';
  position: absolute; inset: 0;
  background: radial-gradient(ellipse 60% 60% at 100% 50%, rgba(17,117,64,0.10) 0%, transparent 100%);
  pointer-events: none;
}
.how-steps {
  margin-top: clamp(32px, 6vh, 56px);
  display: grid; grid-template-columns: 1fr; gap: 0;
  position: relative;
}
@media (min-width: 900px) {
  .how-steps { grid-template-columns: repeat(4,1fr); }
  .how-steps::before {
    content: '';
    position: absolute; top: 36px; left: 12.5%; right: 12.5%;
    height: 1px;
    background: var(--g-brand-h);
    opacity: 0.3; z-index: 0;
  }
}
.how-step {
  background: var(--card-bg);
  border: 1px solid var(--card-border);
  padding: 28px 22px 24px;
  position: relative; z-index: 1;
  opacity: 0; transform: translateY(44px);
}
@media (min-width: 900px) {
  .how-step { border-right: none; }
  .how-step:last-child { border-right: 1px solid var(--card-border); }
}

.how-num { font-family: var(--mono); font-size: 11px; letter-spacing: 0.24em; text-transform: uppercase; margin-bottom: 12px; }
.how-step:nth-child(1) .how-num { color: var(--red-lt); }
.how-step:nth-child(2) .how-num { color: var(--blue-lt); }
.how-step:nth-child(3) .how-num { color: var(--green-lt); }
.how-step:nth-child(4) .how-num { color: var(--red-lt); }

.how-title { font-family: var(--sans); font-size: clamp(18px, 2vw, 22px); font-weight: 800; text-transform: uppercase; color: var(--txt0); line-height: 1.15; margin-bottom: 10px; }
.how-body { font-size: 13.5px; line-height: 1.55; color: var(--txt1); }
.how-body em { color: var(--txt0); font-style: normal; font-family: var(--mono); font-size: 0.9em; }
.how-compound-days { margin-top: 14px; display: flex; gap: 6px; flex-wrap: wrap; }
.how-day { font-family: var(--mono); font-size: 10px; letter-spacing: 0.18em; text-transform: uppercase; padding: 3px 8px; border: 1px solid rgba(196,30,58,0.35); color: var(--red-lt); background: rgba(196,30,58,0.07); }

/* ─── ENGINES ───────────────────────────────────────────────── */
.engines-sec {
  background: var(--bg1);
}
.engines-sec::before {
  content: '';
  position: absolute; inset: 0;
  background:
    radial-gradient(ellipse 50% 70% at 100% 80%, rgba(21,89,163,0.12) 0%, transparent 100%),
    radial-gradient(ellipse 40% 50% at 0% 20%, rgba(196,30,58,0.08) 0%, transparent 100%);
  pointer-events: none;
}
.engines-grid {
  margin-top: clamp(28px, 5vh, 44px);
  display: grid; grid-template-columns: 1fr; gap: 14px;
}
@media (min-width: 900px) {
  .engines-grid { grid-template-columns: 1.1fr 1.3fr 1fr; gap: 0; align-items: start; }
  .engines-grid > .engine + .engine { border-left: 0; }
  .engines-grid > .engine:nth-child(1) { margin-top: 18px; }
  .engines-grid > .engine:nth-child(2) { padding-top: 44px; padding-bottom: 40px; }
  .engines-grid > .engine:nth-child(3) { margin-top: 36px; }
}
.engine {
  background: var(--card-bg); border: 1px solid var(--card-border);
  padding: 32px 24px 24px;
  display: flex; flex-direction: column;
  opacity: 0; transform: translateY(36px);
  transition: border-color .25s, transform .25s;
}
.engine:hover { border-color: var(--txt3); transform: translateY(-2px); }

.engine-icon {
  width: 44px; height: 44px; margin-bottom: 16px;
  object-fit: contain; opacity: 0.80;
  filter: grayscale(0.2);
}
.engine-num { font-family: var(--mono); font-size: 11px; letter-spacing: 0.24em; color: var(--txt3); margin-bottom: 10px; }
.engine.r .engine-num { color: var(--red-lt); }
.engine.b .engine-num { color: var(--blue-lt); }
.engine.g .engine-num { color: var(--green-lt); }
.engine-title { font-family: var(--sans); font-size: clamp(20px, 2.2vw, 26px); font-weight: 800; line-height: 1.1; text-transform: uppercase; color: var(--txt0); }
.engine-title .r { color: var(--red-lt); }
.engine-title .b { color: var(--blue-lt); }
.engine-title .g { color: var(--green-lt); }
.engine-body { font-size: 14px; line-height: 1.55; color: var(--txt1); margin-top: 14px; flex: 1; }
.engine-foot { font-family: var(--mono); font-size: 10px; letter-spacing: 0.2em; color: var(--txt3); margin-top: 18px; padding-top: 12px; border-top: 1px solid var(--card-border); text-transform: uppercase; }

/* ─── COMPARE ───────────────────────────────────────────────── */
.compare-sec {
  background: var(--bg0);
}
.compare-sec::before {
  content: '';
  position: absolute; inset: 0;
  background: url('/assets/maths.jpg') no-repeat center center / cover;
  opacity: 0.06; mix-blend-mode: screen; z-index: 0; pointer-events: none;
}
:root[data-theme="light"] .compare-sec::before { mix-blend-mode: multiply; opacity: 0.04; }
.compare { margin-top: clamp(28px, 5vh, 44px); display: grid; grid-template-columns: 1fr; gap: 28px; position: relative; z-index: 2; }
@media (min-width: 800px) { .compare { grid-template-columns: 1fr auto 1fr; gap: 32px; align-items: start; } }
.cmp-col-title { font-family: var(--sans); font-size: clamp(20px, 2.2vw, 24px); font-weight: 800; letter-spacing: 0.04em; text-transform: uppercase; margin-bottom: 16px; padding-bottom: 8px; border-bottom: 1px solid var(--card-border); }
.cmp-col-title.good { color: var(--green-lt); }
.cmp-col-title.bad  { color: var(--red-lt); }
.ci { font-size: 13.5px; line-height: 1.5; color: var(--txt1); padding: 8px 0 8px 24px; position: relative; border-bottom: 1px dashed rgba(208,220,240,0.06); opacity: 0; }
.ci::before { position: absolute; left: 0; top: 8px; font-family: var(--mono); font-size: 14px; font-weight: 700; }
.ci.good::before { content: '✓'; color: var(--green-lt); }
.ci.bad::before  { content: '✕'; color: var(--red-lt); }
.ci:last-child { border-bottom: none; }
.cmp-vs { display: flex; align-items: center; justify-content: center; }
.cmp-vs .pill { font-family: var(--sans); font-size: 14px; font-weight: 900; color: var(--txt2); letter-spacing: 0.28em; border: 1px solid var(--txt3); padding: 8px 14px; background: var(--card-bg); }