.htb-hero {
  position: relative;
  overflow: hidden;
  padding: clamp(4.5rem, 9vw, 8rem) 0 3rem;
}

.htb-hero::before {
  content: "";
  position: absolute;
  inset: -20% -10% auto auto;
  width: 560px;
  height: 560px;
  border-radius: 50%;
  background: radial-gradient(circle, rgba(159,239,0,.11), transparent 68%);
  pointer-events: none;
}

.htb-hero-grid {
  position: relative;
  display: grid;
  grid-template-columns: minmax(0, 1.15fr) minmax(300px, .85fr);
  gap: clamp(2rem, 6vw, 6rem);
  align-items: center;
}

.htb-hero h1 {
  margin: 0;
  max-width: 900px;
  font-size: clamp(3rem, 7vw, 6rem);
  line-height: .98;
  letter-spacing: -.055em;
}

.htb-hero h1 span {
  display: block;
  color: #9fef00;
}

.htb-hero p {
  max-width: 760px;
  margin: 1.5rem 0 0;
  color: #bdc7d5;
  font-size: clamp(1.05rem, 2vw, 1.24rem);
}

.htb-mark {
  display: grid;
  place-items: center;
  min-height: 310px;
  padding: 2rem;
  border: 1px solid var(--border);
  border-radius: calc(var(--radius) + 4px);
  background:
    linear-gradient(rgba(159,239,0,.035) 1px, transparent 1px),
    linear-gradient(90deg, rgba(159,239,0,.035) 1px, transparent 1px),
    radial-gradient(circle at 50% 50%, rgba(159,239,0,.11), transparent 55%),
    rgba(255,255,255,.02);
  background-size: 28px 28px, 28px 28px, auto, auto;
  box-shadow: var(--shadow);
}

.htb-mark img {
  max-width: 76%;
  max-height: 170px;
  object-fit: contain;
  filter: drop-shadow(0 22px 35px rgba(0,0,0,.42));
}

.library-intro {
  display: flex;
  justify-content: space-between;
  gap: 2rem;
  align-items: end;
  margin-bottom: 2rem;
}

.library-intro h2 {
  margin: 0;
  max-width: 760px;
  font-size: clamp(2.2rem, 5vw, 4rem);
  line-height: 1.04;
  letter-spacing: -.045em;
}

.library-intro p {
  max-width: 540px;
  margin: 0;
  color: var(--muted);
}

.difficulty-grid-modern {
  display: grid;
  grid-template-columns: repeat(2, minmax(0, 1fr));
  gap: 1.2rem;
}

.difficulty-card {
  position: relative;
  overflow: hidden;
  min-height: 280px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  padding: clamp(1.5rem, 3vw, 2.2rem);
  border: 1px solid var(--border);
  border-radius: calc(var(--radius) + 2px);
  color: var(--text);
  background: linear-gradient(145deg, rgba(255,255,255,.05), rgba(255,255,255,.015));
  text-decoration: none;
  transition: transform .25s ease, border-color .25s ease, background .25s ease;
}

.difficulty-card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: radial-gradient(circle at 85% 15%, var(--tier-glow), transparent 36%);
  opacity: .75;
  pointer-events: none;
}

.difficulty-card::after {
  content: "";
  position: absolute;
  inset: 0 auto auto 0;
  width: 100%;
  height: 2px;
  background: linear-gradient(90deg, var(--tier), transparent 72%);
}

.difficulty-card:hover,
.difficulty-card:focus-visible {
  transform: translateY(-7px);
  border-color: var(--tier);
  background: linear-gradient(145deg, rgba(255,255,255,.065), rgba(255,255,255,.02));
}

.difficulty-card.easy { --tier: #42d392; --tier-glow: rgba(66,211,146,.16); }
.difficulty-card.medium { --tier: #f2c94c; --tier-glow: rgba(242,201,76,.15); }
.difficulty-card.hard { --tier: #ff7a18; --tier-glow: rgba(255,122,24,.16); }
.difficulty-card.insane { --tier: #ef5350; --tier-glow: rgba(239,83,80,.16); }

.difficulty-card-top,
.difficulty-card-bottom {
  position: relative;
  z-index: 1;
}

.difficulty-number {
  display: inline-flex;
  width: 46px;
  height: 46px;
  align-items: center;
  justify-content: center;
  border: 1px solid color-mix(in srgb, var(--tier) 45%, transparent);
  border-radius: 13px;
  color: var(--tier);
  background: color-mix(in srgb, var(--tier) 8%, transparent);
  font-family: "IBM Plex Mono", monospace;
  font-weight: 700;
}

.difficulty-card h3 {
  margin: 1.4rem 0 .6rem;
  font-size: clamp(2rem, 4vw, 3rem);
  letter-spacing: -.04em;
}

.difficulty-card p {
  max-width: 530px;
  margin: 0;
  color: #aeb9c8;
}

.difficulty-card-bottom {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  margin-top: 2rem;
  color: var(--tier);
  font-family: "IBM Plex Mono", monospace;
  font-size: .82rem;
  font-weight: 700;
  letter-spacing: .04em;
  text-transform: uppercase;
}

.library-note {
  display: grid;
  grid-template-columns: auto 1fr;
  gap: 1rem;
  align-items: start;
  padding: 1.4rem;
  border: 1px solid rgba(159,239,0,.22);
  border-radius: var(--radius);
  background: rgba(159,239,0,.045);
}

.library-note i {
  width: 42px;
  height: 42px;
  display: grid;
  place-items: center;
  border-radius: 11px;
  color: #9fef00;
  background: rgba(159,239,0,.08);
}

.library-note strong { display: block; margin-bottom: .25rem; }
.library-note p { margin: 0; color: var(--muted); }

@media (max-width: 940px) {
  .htb-hero-grid { grid-template-columns: 1fr; }
  .htb-mark { min-height: 240px; }
  .library-intro { align-items: start; flex-direction: column; }
}

@media (max-width: 720px) {
  .difficulty-grid-modern { grid-template-columns: 1fr; }
  .difficulty-card { min-height: 245px; }
}