/* ============================================================
   ARBOROPS — DESIGN SYSTEM v3
   Palette: Near-Black × Electric Indigo × White
   Vibe: YC / a16z — operator credibility, technical authority
   ============================================================ */

@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800;900&family=DM+Mono:wght@400;500&display=swap');

/* ── TOKENS ── */
:root {
  --bg:          #08090E;
  --surface:     #0D0F18;
  --surface-2:   #131520;
  --border:      rgba(255, 255, 255, 0.07);
  --border-hi:   rgba(255, 255, 255, 0.14);
  --accent:      #6366F1;        /* electric indigo */
  --accent-dim:  rgba(99, 102, 241, 0.15);
  --accent-glow: rgba(99, 102, 241, 0.35);
  --white:       #FFFFFF;
  --offwhite:    #E8E9EF;
  --muted:       #4B4D5E;
  --muted-light: #8B8FA8;
  --font-main:   'Inter', system-ui, sans-serif;
  --font-mono:   'DM Mono', 'Menlo', monospace;
  --ease:        cubic-bezier(0.16, 1, 0.3, 1);
}

/* ── RESET ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  background: var(--bg);
  color: var(--offwhite);
  font-family: var(--font-main);
  font-size: 16px;
  line-height: 1.6;
  overflow-x: hidden;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}
a { color: inherit; text-decoration: none; }
img { display: block; max-width: 100%; }
ul { list-style: none; }

/* ── UTILITY ── */
.container {
  width: 100%;
  max-width: 1120px;
  margin: 0 auto;
  padding: 0 2rem;
}

/* Scroll-reveal */
.reveal {
  opacity: 0;
  transform: translateY(24px);
  transition: opacity 0.65s var(--ease), transform 0.65s var(--ease);
}
.reveal.visible { opacity: 1; transform: none; }
.reveal-delay-1 { transition-delay: 0.08s; }
.reveal-delay-2 { transition-delay: 0.16s; }
.reveal-delay-3 { transition-delay: 0.24s; }

/* ============================================================
   NAV
   ============================================================ */
#nav {
  position: fixed;
  top: 0; left: 0; right: 0;
  z-index: 100;
  padding: 1.1rem 0;
  transition: background 0.3s ease, border-color 0.3s ease;
  border-bottom: 1px solid transparent;
}
#nav.scrolled {
  background: rgba(8, 9, 14, 0.88);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom-color: var(--border);
}
.nav-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
}
.nav-logo {
  font-family: var(--font-main);
  font-size: 0.88rem;
  font-weight: 700;
  letter-spacing: 0.22em;
  color: var(--white);
  text-transform: uppercase;
}
.nav-links {
  display: flex;
  align-items: center;
  gap: 2.25rem;
}
.nav-links a {
  font-size: 0.78rem;
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--muted-light);
  transition: color 0.15s;
}
.nav-links a:hover { color: var(--white); }
.nav-cta {
  font-size: 0.78rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  padding: 0.55rem 1.25rem;
  background: var(--accent);
  color: var(--white);
  transition: opacity 0.2s, transform 0.15s;
}
.nav-cta:hover { opacity: 0.88; transform: translateY(-1px); }

/* Hamburger */
.hamburger {
  display: none;
  flex-direction: column;
  gap: 5px;
  cursor: pointer;
  padding: 4px;
  background: none;
  border: none;
}
.hamburger span {
  display: block;
  width: 22px;
  height: 1.5px;
  background: var(--offwhite);
  transition: all 0.3s var(--ease);
}
.hamburger.open span:nth-child(1) { transform: translateY(6.5px) rotate(45deg); }
.hamburger.open span:nth-child(2) { opacity: 0; }
.hamburger.open span:nth-child(3) { transform: translateY(-6.5px) rotate(-45deg); }

/* Mobile menu */
.mobile-menu {
  display: none;
  flex-direction: column;
  gap: 0;
  background: rgba(8, 9, 14, 0.98);
  border-top: 1px solid var(--border);
  position: fixed;
  top: 57px; left: 0; right: 0;
  z-index: 99;
}
.mobile-menu.open { display: flex; }
.mobile-menu a {
  font-size: 0.85rem;
  font-weight: 500;
  letter-spacing: 0.04em;
  color: var(--muted-light);
  padding: 1rem 1.5rem;
  border-bottom: 1px solid var(--border);
  transition: color 0.15s, background 0.15s;
}
.mobile-menu a:hover { color: var(--white); background: var(--surface); }
.mobile-menu a:last-child { border-bottom: none; }

/* ============================================================
   HERO
   ============================================================ */
#hero {
  min-height: 100svh;
  display: flex;
  align-items: center;
  position: relative;
  overflow: hidden;
  padding-top: 5rem;
}
/* Subtle grid lines — technical, precise */
.hero-bg {
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background-image:
    linear-gradient(rgba(255,255,255,0.03) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.03) 1px, transparent 1px);
  background-size: 80px 80px;
  mask-image: radial-gradient(ellipse 80% 70% at 50% 0%, black 20%, transparent 100%);
}
/* Accent pulse — bottom-left, not centred */
.hero-bg::after {
  content: '';
  position: absolute;
  bottom: -10%;
  left: -5%;
  width: 500px;
  height: 500px;
  background: radial-gradient(ellipse at center, rgba(99, 102, 241, 0.12) 0%, transparent 65%);
  pointer-events: none;
}
.hero-inner {
  position: relative;
  z-index: 1;
  max-width: 900px;
}
.hero-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 0.6rem;
  margin-bottom: 2rem;
  padding: 0.3rem 0.75rem;
  border: 1px solid var(--border-hi);
  background: var(--surface);
}
.hero-eyebrow-dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--accent);
  animation: pulse 2.5s ease-in-out infinite;
}
@keyframes pulse {
  0%, 100% { opacity: 1; transform: scale(1); }
  50% { opacity: 0.5; transform: scale(0.85); }
}
.hero-eyebrow-text {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  font-weight: 400;
  letter-spacing: 0.06em;
  color: var(--muted-light);
}
.hero-title {
  font-family: var(--font-main);
  font-size: clamp(2.6rem, 6.5vw, 5.2rem);
  font-weight: 800;
  line-height: 1.06;
  color: var(--white);
  margin-bottom: 1.5rem;
  letter-spacing: -0.03em;
}
.hero-title em {
  font-style: normal;
  color: var(--accent);
}
.hero-sub {
  font-size: 1.05rem;
  font-weight: 400;
  color: var(--muted-light);
  max-width: 520px;
  line-height: 1.75;
  margin-bottom: 2.75rem;
  letter-spacing: 0.01em;
}
.hero-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}
.btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--font-main);
  font-size: 0.82rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 0.8rem 1.75rem;
  background: var(--accent);
  color: var(--white);
  transition: opacity 0.2s, transform 0.15s;
}
.btn-primary:hover { opacity: 0.88; transform: translateY(-1px); }
.btn-ghost {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
  font-family: var(--font-main);
  font-size: 0.82rem;
  font-weight: 500;
  letter-spacing: 0.02em;
  color: var(--muted-light);
  transition: color 0.15s;
}
.btn-ghost:hover { color: var(--white); }
.btn-ghost svg { transition: transform 0.2s; }
.btn-ghost:hover svg { transform: translateX(3px); }

/* Scroll indicator */
.hero-scroll {
  position: absolute;
  bottom: 2rem;
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.4rem;
  z-index: 1;
}
.hero-scroll-text {
  font-family: var(--font-mono);
  font-size: 0.6rem;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  color: var(--muted);
}
.hero-scroll-line {
  width: 1px;
  height: 36px;
  background: linear-gradient(to bottom, var(--accent), transparent);
  animation: scrollLine 2s ease-in-out infinite;
}
@keyframes scrollLine {
  0%, 100% { opacity: 0.3; }
  50% { opacity: 0.9; }
}

/* ============================================================
   PHILOSOPHY STRIP
   ============================================================ */
#philosophy {
  padding: 4rem 0;
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
  background: var(--surface);
}
.philosophy-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 0;
}
.philosophy-item {
  padding: 2rem 2rem;
  border-right: 1px solid var(--border);
}
.philosophy-item:last-child { border-right: none; }
.philosophy-num {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  color: var(--accent);
  line-height: 1;
  margin-bottom: 1rem;
  text-transform: uppercase;
}
.philosophy-title {
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: var(--white);
  margin-bottom: 0.6rem;
}
.philosophy-text {
  font-size: 0.875rem;
  color: var(--muted-light);
  line-height: 1.7;
  font-weight: 400;
}

/* ============================================================
   SHARED SECTION ELEMENTS
   ============================================================ */
.section-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1rem;
}
.section-eyebrow-line {
  width: 16px;
  height: 2px;
  background: var(--accent);
}
.section-eyebrow-text {
  font-family: var(--font-mono);
  font-size: 0.68rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
}
.section-title {
  font-family: var(--font-main);
  font-size: clamp(1.85rem, 4vw, 2.9rem);
  font-weight: 800;
  line-height: 1.12;
  color: var(--white);
  margin-bottom: 1rem;
  letter-spacing: -0.025em;
}
.section-sub {
  font-size: 0.95rem;
  color: var(--muted-light);
  font-weight: 400;
  max-width: 480px;
  line-height: 1.8;
  margin-bottom: 3.5rem;
}

/* ============================================================
   SOLUTIONS
   ============================================================ */
#solutions {
  padding-top: 6rem;
  padding-bottom: 0;
}
#solutions > .container {
  padding-bottom: 4rem;
}
.solution-row {
  padding: 4.5rem 0;
  border-top: 1px solid var(--border);
}
.solution-row:last-of-type {
  border-bottom: 1px solid var(--border);
}
.solution-row-inner {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 4.5rem;
  align-items: center;
}
/* Flip: content left, image right */
.solution-row--flip .solution-row-inner {
  direction: rtl;
}
.solution-row--flip .solution-row-inner > * {
  direction: ltr;
}

/* Image */
.solution-img-wrap {
  position: relative;
  border: 1px solid var(--border);
  overflow: hidden;
  background: var(--surface);
}
.solution-img-wrap img {
  width: 100%;
  height: auto;
  display: block;
  transition: transform 0.6s var(--ease);
}
.solution-img-wrap:hover img { transform: scale(1.025); }
.solution-img-badge {
  position: absolute;
  bottom: 0; left: 0; right: 0;
  padding: 0.5rem 0.85rem;
  background: rgba(8, 9, 14, 0.88);
  backdrop-filter: blur(8px);
  border-top: 1px solid var(--border);
  font-family: var(--font-mono);
  font-size: 0.62rem;
  font-weight: 400;
  letter-spacing: 0.06em;
  color: var(--accent);
}

/* Content */
.solution-tag {
  display: inline-block;
  font-family: var(--font-mono);
  font-size: 0.62rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--accent);
  border: 1px solid rgba(99, 102, 241, 0.3);
  padding: 0.2rem 0.55rem;
  margin-bottom: 1rem;
  background: var(--accent-dim);
}
.solution-row-title {
  font-family: var(--font-main);
  font-size: clamp(1.25rem, 2.5vw, 1.7rem);
  font-weight: 700;
  color: var(--white);
  line-height: 1.22;
  margin-bottom: 1.5rem;
  letter-spacing: -0.02em;
}
.solution-row-problem {
  font-size: 0.875rem;
  color: var(--muted-light);
  line-height: 1.75;
  font-weight: 400;
  margin-bottom: 1rem;
  padding-left: 0.875rem;
  border-left: 2px solid var(--accent);
}
.solution-problem-label {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.62rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.3rem;
}
.solution-row-body {
  font-size: 0.875rem;
  color: var(--muted-light);
  line-height: 1.8;
  font-weight: 400;
  margin-bottom: 2rem;
}
.solution-row-body em {
  color: var(--offwhite);
  font-style: italic;
}
/* Impact metrics */
.solution-metrics {
  display: flex;
  gap: 0;
  border: 1px solid var(--border);
  background: var(--surface);
}
.solution-metric {
  flex: 1;
  padding: 0.9rem 1rem;
  border-right: 1px solid var(--border);
  text-align: center;
}
.solution-metric:last-child { border-right: none; }
.solution-metric-value {
  display: block;
  font-family: var(--font-main);
  font-size: 1.3rem;
  font-weight: 700;
  color: var(--white);
  line-height: 1;
  margin-bottom: 0.25rem;
  letter-spacing: -0.02em;
}
.solution-metric-label {
  display: block;
  font-family: var(--font-mono);
  font-size: 0.6rem;
  font-weight: 400;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--muted);
}

/* ============================================================
   HOW WE WORK
   ============================================================ */
#process {
  padding: 6rem 0;
  background: var(--surface);
  border-top: 1px solid var(--border);
  border-bottom: 1px solid var(--border);
}
.process-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5rem;
  align-items: start;
}
.process-left .section-title { margin-bottom: 0.75rem; }
.process-left .section-sub { margin-bottom: 0; }
.process-steps { display: flex; flex-direction: column; }
.process-step {
  display: grid;
  grid-template-columns: 40px 1fr;
  gap: 1rem;
  padding: 1.5rem 0;
  border-bottom: 1px solid var(--border);
}
.process-step:last-child { border-bottom: none; }
.process-step-num {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  color: var(--accent);
  padding-top: 0.15rem;
  text-transform: uppercase;
}
.process-step-title {
  font-size: 0.82rem;
  font-weight: 700;
  letter-spacing: 0.01em;
  color: var(--white);
  margin-bottom: 0.35rem;
}
.process-step-text {
  font-size: 0.875rem;
  color: var(--muted-light);
  line-height: 1.75;
  font-weight: 400;
}

/* ============================================================
   CONTACT
   ============================================================ */
#contact {
  padding: 6rem 0;
}
.contact-layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 5rem;
  align-items: start;
}
.contact-left .section-title { margin-bottom: 0.75rem; }
.contact-detail { margin-top: 2rem; }
.contact-detail-label {
  font-family: var(--font-mono);
  font-size: 0.62rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 0.35rem;
}
.contact-detail-value {
  font-size: 0.925rem;
  color: var(--muted-light);
  font-weight: 400;
}
.contact-detail-value a {
  color: var(--accent);
  transition: color 0.15s;
}
.contact-detail-value a:hover { color: var(--white); }
.contact-note {
  margin-top: 2.5rem;
  padding: 1.1rem 1.25rem;
  border: 1px solid var(--border);
  border-left: 2px solid var(--accent);
  background: var(--surface);
}
.contact-note-title {
  font-family: var(--font-mono);
  font-size: 0.65rem;
  font-weight: 500;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--accent);
  margin-bottom: 0.4rem;
}
.contact-note-text {
  font-size: 0.85rem;
  color: var(--muted-light);
  line-height: 1.65;
  font-weight: 400;
}

/* Form */
.contact-form { display: flex; flex-direction: column; gap: 0.85rem; }
.form-group { display: flex; flex-direction: column; gap: 0.35rem; }
.form-row { display: grid; grid-template-columns: 1fr 1fr; gap: 0.85rem; }
.form-label {
  font-family: var(--font-mono);
  font-size: 0.62rem;
  font-weight: 500;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--muted);
}
.form-input {
  background: var(--surface);
  border: 1px solid var(--border);
  color: var(--offwhite);
  font-family: var(--font-main);
  font-size: 0.9rem;
  font-weight: 400;
  padding: 0.8rem 0.9rem;
  width: 100%;
  transition: border-color 0.2s, background 0.2s;
  outline: none;
  -webkit-appearance: none;
  border-radius: 0;
}
.form-input::placeholder { color: var(--muted); }
.form-input:focus {
  border-color: var(--accent);
  background: var(--surface-2);
}
textarea.form-input { resize: vertical; min-height: 110px; }
.form-submit {
  font-family: var(--font-main);
  font-size: 0.82rem;
  font-weight: 600;
  letter-spacing: 0.02em;
  padding: 0.9rem 2rem;
  background: var(--accent);
  color: var(--white);
  border: none;
  cursor: pointer;
  width: 100%;
  transition: opacity 0.2s, transform 0.15s;
  margin-top: 0.35rem;
  border-radius: 0;
}
.form-submit:hover { opacity: 0.88; transform: translateY(-1px); }
.form-submit:disabled { opacity: 0.5; cursor: not-allowed; transform: none; }
.form-message {
  font-size: 0.82rem;
  padding: 0.7rem 0.9rem;
  border: 1px solid transparent;
  font-family: var(--font-mono);
  display: none;
}
.form-message.success {
  color: #6EE7B7;
  border-color: rgba(110, 231, 183, 0.2);
  background: rgba(110, 231, 183, 0.05);
  display: block;
}
.form-message.error {
  color: #FCA5A5;
  border-color: rgba(252, 165, 165, 0.2);
  background: rgba(252, 165, 165, 0.05);
  display: block;
}

/* ============================================================
   FOOTER
   ============================================================ */
footer {
  padding: 2rem 0;
  border-top: 1px solid var(--border);
}
.footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 0.75rem;
}
.footer-logo {
  font-family: var(--font-main);
  font-size: 0.75rem;
  font-weight: 700;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--muted);
}
.footer-copy {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--muted);
  letter-spacing: 0.03em;
}
.footer-email {
  font-family: var(--font-mono);
  font-size: 0.7rem;
  color: var(--muted);
  transition: color 0.15s;
}
.footer-email:hover { color: var(--accent); }

/* ============================================================
   RESPONSIVE — 900px
   ============================================================ */
@media (max-width: 900px) {
  .philosophy-grid { grid-template-columns: 1fr; }
  .philosophy-item { border-right: none; border-bottom: 1px solid var(--border); }
  .philosophy-item:last-child { border-bottom: none; }
  .solution-row-inner { grid-template-columns: 1fr; gap: 2rem; }
  .solution-row--flip .solution-row-inner { direction: ltr; }
  .solution-row { padding: 3.5rem 0; }
  .process-layout, .contact-layout { grid-template-columns: 1fr; gap: 2.5rem; }
  .process-left .section-sub { margin-bottom: 1.5rem; }
  .nav-links { display: none; }
  .nav-cta { display: none; }
  .hamburger { display: flex; }
  #process, #contact { padding: 4.5rem 0; }
}

/* ============================================================
   RESPONSIVE — 600px
   ============================================================ */
@media (max-width: 600px) {
  .container { padding: 0 1.25rem; }
  #solutions, #process, #contact { padding: 3.5rem 0; }
  #solutions > .container { padding-bottom: 2.5rem; }
  .section-sub { margin-bottom: 2rem; }
  .hero-title { font-size: clamp(2rem, 11vw, 2.8rem); letter-spacing: -0.025em; }
  .hero-sub { font-size: 0.95rem; }
  .hero-actions { gap: 0.75rem; }
  .philosophy-item { padding: 1.75rem 1.25rem; }
  .solution-row { padding: 2.75rem 0; }
  .solution-metrics { flex-direction: column; }
  .solution-metric { border-right: none; border-bottom: 1px solid var(--border); padding: 0.75rem 1rem; }
  .solution-metric:last-child { border-bottom: none; }
  .form-row { grid-template-columns: 1fr; }
  .contact-layout { gap: 2.5rem; }
  .contact-note { margin-top: 1.5rem; }
  .process-step { grid-template-columns: 36px 1fr; gap: 0.75rem; padding: 1.25rem 0; }
  .form-input { padding: 0.85rem; }
  .form-submit { padding: 1rem; }
  .footer-inner { flex-direction: column; align-items: flex-start; gap: 0.5rem; }
  #philosophy { padding: 3rem 0; }
}

/* ============================================================
   MICRO-INTERACTION & UX ELEMENTS
   ============================================================ */

/* Scroll progress bar */
#scroll-progress {
  position: fixed;
  top: 0; left: 0;
  height: 2px;
  width: 0%;
  background: var(--accent);
  z-index: 200;
  transition: width 0.1s linear;
  pointer-events: none;
}

/* Active nav link */
.nav-links a.active {
  color: var(--white);
}
.nav-links a.active::after {
  content: '';
  display: block;
  width: 100%;
  height: 1px;
  background: var(--accent);
  margin-top: 2px;
}

/* Copy email button */
.contact-detail-value {
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.copy-email-btn {
  background: none;
  border: 1px solid var(--border);
  color: var(--muted);
  cursor: pointer;
  padding: 0.3rem 0.4rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  transition: color 0.15s, border-color 0.15s, background 0.15s;
  line-height: 1;
}
.copy-email-btn:hover {
  color: var(--accent);
  border-color: rgba(99, 102, 241, 0.4);
  background: var(--accent-dim);
}
.copy-email-btn.copied {
  color: #6EE7B7;
  border-color: rgba(110, 231, 183, 0.3);
  background: rgba(110, 231, 183, 0.06);
}
/* Tooltip "Copied!" state via pseudo */
.copy-email-btn.copied::after {
  content: 'Copied';
  position: absolute;
  bottom: calc(100% + 6px);
  left: 50%;
  transform: translateX(-50%);
  font-family: var(--font-mono);
  font-size: 0.6rem;
  background: #6EE7B7;
  color: #08090E;
  padding: 0.2rem 0.4rem;
  white-space: nowrap;
  pointer-events: none;
}
.copy-email-btn { position: relative; }

/* Process step hover */
.process-step {
  transition: border-color 0.2s;
}
.process-step:hover .process-step-num {
  color: var(--accent);
}
.process-step:hover .process-step-title {
  color: var(--white);
}

/* Back to top button */
#back-to-top {
  position: fixed;
  bottom: 2rem;
  right: 2rem;
  z-index: 90;
  width: 40px;
  height: 40px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--muted-light);
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  pointer-events: none;
  transition: opacity 0.3s, color 0.15s, border-color 0.15s, transform 0.2s;
}
#back-to-top.visible {
  opacity: 1;
  pointer-events: auto;
}
#back-to-top:hover {
  color: var(--accent);
  border-color: rgba(99, 102, 241, 0.4);
  transform: translateY(-2px);
}

/* Solution card image hover — subtle brightness lift */
.solution-img-wrap::after {
  content: '';
  position: absolute;
  inset: 0;
  background: rgba(99, 102, 241, 0.05);
  opacity: 0;
  transition: opacity 0.3s;
  pointer-events: none;
}
.solution-img-wrap:hover::after {
  opacity: 1;
}