/* ============================================
   Cognia — Design tokens
   ============================================ */
:root {
  /* Color */
  --color-primary: #0F172A;
  --color-primary-foreground: #FFFFFF;
  --color-secondary: #334155;
  --color-accent-start: #4F6BFF;
  --color-accent-end: #7C3AED;
  --color-accent: #4F5BEE;
  --color-background: #F8FAFC;
  --color-surface: #FFFFFF;
  --color-foreground: #0F172A;
  --color-muted: #5B6578;
  --color-muted-bg: #F1F5F9;
  --color-border: #E2E8F0;
  --color-destructive: #DC2626;
  --color-success: #15803D;
  --color-ring: #4F5BEE;

  --gradient-accent: linear-gradient(135deg, var(--color-accent-start), var(--color-accent-end));
  --gradient-navy: radial-gradient(ellipse 900px 500px at 15% -10%, rgba(79,107,255,.35), transparent 60%),
                    radial-gradient(ellipse 700px 500px at 100% 0%, rgba(124,58,237,.30), transparent 55%),
                    linear-gradient(180deg, #0B1220 0%, #0F172A 100%);

  /* Type */
  --font-sans: 'Plus Jakarta Sans', 'Segoe UI', Arial, sans-serif;
  --text-xs: 0.8125rem;
  --text-sm: 0.9375rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;
  --text-4xl: 2.375rem;
  --text-5xl: 3rem;
  --text-6xl: 3.75rem;

  /* Space (4pt scale) */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.25rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-10: 2.5rem;
  --space-12: 3rem;
  --space-16: 4rem;
  --space-20: 5rem;
  --space-24: 6rem;
  --space-32: 8rem;

  /* Radius */
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 22px;
  --radius-full: 999px;

  /* Shadow */
  --shadow-sm: 0 1px 2px rgba(15, 23, 42, 0.06);
  --shadow-md: 0 8px 24px rgba(15, 23, 42, 0.08);
  --shadow-lg: 0 20px 48px rgba(15, 23, 42, 0.14);

  /* Motion */
  --ease-out: cubic-bezier(0.16, 1, 0.3, 1);
  --duration-fast: 150ms;
  --duration-base: 250ms;

  --header-h: 76px;
}

/* ============================================
   Reset
   ============================================ */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--text-base);
  line-height: 1.6;
  color: var(--color-foreground);
  background: var(--color-background);
  -webkit-font-smoothing: antialiased;
}

img { max-width: 100%; display: block; }
ul, ol { list-style: none; margin: 0; padding: 0; }
a { color: inherit; text-decoration: none; }
button { font-family: inherit; }

h1, h2, h3, h4 {
  margin: 0;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.15;
}

:focus-visible {
  outline: 2.5px solid var(--color-ring);
  outline-offset: 3px;
  border-radius: 4px;
}

.skip-link {
  position: absolute;
  left: -9999px;
  top: 0;
  background: var(--color-primary);
  color: #fff;
  padding: var(--space-3) var(--space-5);
  border-radius: var(--radius-sm);
  z-index: 200;
}
.skip-link:focus {
  left: var(--space-4);
  top: var(--space-4);
}

.container {
  width: 100%;
  max-width: 1180px;
  margin-inline: auto;
  padding-inline: var(--space-6);
}

@media (max-width: 640px) {
  .container { padding-inline: var(--space-5); }
}

/* ============================================
   Buttons
   ============================================ */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  font-weight: 600;
  font-size: var(--text-base);
  padding: 0.85rem 1.5rem;
  border-radius: var(--radius-full);
  border: 1px solid transparent;
  cursor: pointer;
  transition: transform var(--duration-fast) var(--ease-out),
              box-shadow var(--duration-fast) var(--ease-out),
              background var(--duration-fast) var(--ease-out),
              border-color var(--duration-fast) var(--ease-out);
  white-space: nowrap;
}
.btn svg { flex-shrink: 0; }

.btn-primary {
  position: relative;
  background: var(--gradient-accent);
  color: #fff;
  box-shadow: var(--shadow-sm);
  overflow: hidden;
}
.btn-primary::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(115deg, transparent 30%, rgba(255,255,255,0.35) 45%, transparent 60%);
  transform: translateX(-100%);
  transition: transform 550ms var(--ease-out);
}
.btn-primary:hover::after { transform: translateX(100%); }
.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: var(--shadow-md);
}
.btn-primary:active { transform: translateY(0); }

.btn-ghost {
  background: transparent;
  color: var(--color-foreground);
  border-color: var(--color-border);
}
.btn-ghost:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
}

.btn-lg { padding: 1rem 1.9rem; font-size: var(--text-lg); }
.btn-sm { padding: 0.6rem 1.2rem; font-size: var(--text-sm); }

/* Magnetic buttons: JS drives transform via inline style on mousemove/leave.
   Exclude transform from the CSS transition so it doesn't fight GSAP's tween. */
.magnetic {
  transition: box-shadow var(--duration-fast) var(--ease-out),
              background var(--duration-fast) var(--ease-out),
              border-color var(--duration-fast) var(--ease-out);
  will-change: transform;
}
/* When JS is active it sets transform inline (which always wins over this
   rule's specificity), overriding the plain CSS lift below with the
   magnetic pull. This is just the no-JS/GSAP-failed fallback. */

/* ============================================
   Scroll progress bar
   ============================================ */
.scroll-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 3px;
  background: var(--gradient-accent);
  transform: scaleX(0);
  transform-origin: 0 50%;
  z-index: 200;
  will-change: transform;
}

/* ============================================
   Header / Nav
   ============================================ */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  border-bottom: 1px solid var(--color-border);
  transition: box-shadow var(--duration-base) var(--ease-out);
}
/* Blur lives on a pseudo-element (not on .site-header itself) because
   backdrop-filter on an ancestor makes WebKit treat it as the containing
   block for position:fixed descendants — which broke the fixed mobile
   nav panel's height. */
.site-header::before {
  content: "";
  position: absolute;
  inset: 0;
  z-index: -1;
  background: rgba(248, 250, 252, 0.82);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
}
.site-header.is-scrolled {
  box-shadow: var(--shadow-sm);
}
.site-header.is-scrolled .header-inner {
  height: calc(var(--header-h) - 14px);
}

.header-inner {
  height: var(--header-h);
  display: flex;
  align-items: center;
  justify-content: space-between;
  transition: height var(--duration-base) var(--ease-out);
}

.brand { display: inline-flex; align-items: center; }

.main-nav {
  display: flex;
  align-items: center;
  gap: var(--space-8);
}

.main-nav ul {
  display: flex;
  gap: var(--space-6);
}

.main-nav a:not(.btn) {
  font-weight: 500;
  font-size: var(--text-sm);
  color: var(--color-secondary);
  padding: var(--space-2) 0;
  border-bottom: 2px solid transparent;
  transition: color var(--duration-fast) var(--ease-out), border-color var(--duration-fast) var(--ease-out);
}
.main-nav a:not(.btn):hover {
  color: var(--color-primary);
  border-bottom-color: var(--color-accent);
}
.main-nav a:not(.btn).is-active {
  color: var(--color-primary);
  border-bottom-color: var(--color-accent);
}

.nav-toggle {
  display: none;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-surface);
  color: var(--color-primary);
  cursor: pointer;
}

@media (max-width: 860px) {
  .nav-toggle { display: inline-flex; }

  .main-nav {
    position: fixed;
    inset: var(--header-h) 0 0 0;
    background: var(--color-surface);
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: var(--space-8) var(--space-6);
    transform: translateX(100%);
    transition: transform var(--duration-base) var(--ease-out);
    overflow-y: auto;
  }
  .main-nav.is-open { transform: translateX(0); }

  .main-nav ul {
    flex-direction: column;
    gap: var(--space-1);
    margin-bottom: var(--space-8);
  }
  .main-nav ul a { display: block; padding: var(--space-4) 0; font-size: var(--text-lg); border-bottom: 1px solid var(--color-border); }
  .nav-cta { justify-content: center; }
}

/* ============================================
   Hero
   ============================================ */
.hero {
  position: relative;
  background: var(--gradient-navy);
  color: #fff;
  /* El padding inferior es mayor que el superior a propósito: deja lugar
     al scroll-cue (indicador "Desplázate") sin que se solape con
     .hero-points, que es el último elemento del contenido. */
  padding-block: var(--space-24) var(--space-32);
  text-align: center;
  overflow: hidden;
}

.hero-bg {
  position: absolute;
  inset: 0;
  z-index: 0;
  overflow: hidden;
  pointer-events: none;
}
.particle-canvas {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  display: block;
}
/* Moving particles are exactly the kind of motion reduced-motion users want
   to skip — hide the canvas and let the static gradient carry the hero. */
@media (prefers-reduced-motion: reduce) {
  .particle-canvas { display: none; }
}

.hero-grid {
  position: absolute;
  inset: 0;
  background-image:
    linear-gradient(rgba(255,255,255,0.04) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,0.04) 1px, transparent 1px);
  background-size: 48px 48px;
  mask-image: radial-gradient(ellipse 60% 60% at 50% 30%, #000 40%, transparent 90%);
}

.hero-inner { position: relative; z-index: 1; max-width: 780px; }

.hero-anim { opacity: 0; }

.text-gradient {
  background: linear-gradient(90deg, #93A9FF, #C4B5FD, #93A9FF);
  background-size: 200% auto;
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
  animation: text-gradient-shift 6s ease-in-out infinite;
}
@media (prefers-reduced-motion: reduce) {
  .text-gradient { animation: none; }
}
@keyframes text-gradient-shift {
  0%, 100% { background-position: 0% 50%; }
  50% { background-position: 100% 50%; }
}

.eyebrow {
  display: inline-block;
  font-size: var(--text-sm);
  font-weight: 600;
  letter-spacing: 0.04em;
  color: var(--color-accent-start);
  margin-bottom: var(--space-4);
}
.hero .eyebrow {
  color: #C7D2FE;
  background: rgba(255,255,255,0.08);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-full);
  border: 1px solid rgba(255,255,255,0.14);
}

.hero h1 {
  font-size: var(--text-5xl);
  color: #fff;
  margin-bottom: var(--space-5);
}

.hero-lead {
  font-size: var(--text-lg);
  color: #CBD5E1;
  max-width: 620px;
  margin-inline: auto;
  margin-bottom: var(--space-8);
}

.hero-actions {
  display: flex;
  gap: var(--space-4);
  justify-content: center;
  flex-wrap: wrap;
  margin-bottom: var(--space-10);
}
.hero .btn-ghost {
  color: #fff;
  border-color: rgba(255,255,255,0.25);
}
.hero .btn-ghost:hover {
  border-color: #fff;
  color: #fff;
  background: rgba(255,255,255,0.08);
}

.hero-points {
  display: flex;
  gap: var(--space-6);
  justify-content: center;
  flex-wrap: wrap;
  color: #94A3B8;
  font-size: var(--text-sm);
}
.hero-points li { display: flex; align-items: center; gap: var(--space-2); }
.hero-points svg { color: #6EE7B7; }

.scroll-cue {
  position: absolute;
  left: 50%;
  bottom: var(--space-8);
  z-index: 1;
  transform: translateX(-50%);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: var(--space-3);
  color: #94A3B8;
  font-size: var(--text-xs);
  font-weight: 600;
  letter-spacing: 0.15em;
  text-transform: uppercase;
  text-decoration: none;
  transition: opacity var(--duration-base) var(--ease-out), color var(--duration-fast) var(--ease-out);
}
.scroll-cue:hover { color: #fff; }
.scroll-cue.is-hidden { opacity: 0; pointer-events: none; }

.scroll-cue-line {
  position: relative;
  width: 1px;
  height: 44px;
  background: linear-gradient(to bottom, rgba(255, 255, 255, 0.45), transparent);
  overflow: hidden;
}
.scroll-cue-dot {
  position: absolute;
  top: -6px;
  left: 50%;
  width: 5px;
  height: 5px;
  margin-left: -2.5px;
  border-radius: 50%;
  background: var(--gradient-accent);
  animation: scroll-cue-travel 2s ease-in-out infinite;
}
@keyframes scroll-cue-travel {
  0% { transform: translateY(0); opacity: 0; }
  20% { opacity: 1; }
  80% { opacity: 1; }
  100% { transform: translateY(44px); opacity: 0; }
}
@media (prefers-reduced-motion: reduce) {
  .scroll-cue-dot { animation: none; top: 40%; opacity: 1; }
}

@media (max-width: 640px) {
  .hero { padding-block: var(--space-16) var(--space-24); }
  .hero h1 { font-size: var(--text-3xl); }
  .scroll-cue { bottom: var(--space-5); }
  .scroll-cue-line { height: 32px; }
  @keyframes scroll-cue-travel {
    0% { transform: translateY(0); opacity: 0; }
    20% { opacity: 1; }
    80% { opacity: 1; }
    100% { transform: translateY(32px); opacity: 0; }
  }
}

/* ============================================
   Sections
   ============================================ */
.section {
  padding-block: var(--space-24);
}
.section--alt { background: var(--color-muted-bg); }

.section h2 {
  font-size: var(--text-4xl);
  max-width: 640px;
  margin-bottom: var(--space-4);
}
.section-lead {
  color: var(--color-muted);
  font-size: var(--text-lg);
  max-width: 560px;
  margin-bottom: var(--space-12);
}

@media (max-width: 640px) {
  .section { padding-block: var(--space-16); }
  .section h2 { font-size: var(--text-3xl); }
}

/* ============================================
   Bento grid (services)
   ============================================ */
.bento-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: var(--space-5);
  perspective: 1200px;
}
.bento-card {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-8);
  transition: box-shadow var(--duration-base) var(--ease-out), border-color var(--duration-base) var(--ease-out);
  will-change: transform;
}
.bento-card:hover {
  box-shadow: 0 20px 48px -12px rgba(79, 91, 238, 0.28);
  border-color: transparent;
}
.bento-card--wide { grid-column: span 2; }

.card-icon {
  width: 52px;
  height: 52px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  background: var(--gradient-accent);
  transition: transform var(--duration-base) var(--ease-out);
  color: #fff;
  margin-bottom: var(--space-5);
}

.bento-card h3 { font-size: var(--text-xl); margin-bottom: var(--space-2); }
.bento-card p { color: var(--color-muted); margin: 0; }
.bento-card:hover .card-icon { transform: scale(1.08) rotate(-4deg); }

@media (max-width: 860px) {
  .bento-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 640px) {
  .bento-grid { grid-template-columns: 1fr; }
  .bento-card--wide { grid-column: span 1; }
}

/* ============================================
   Process
   ============================================ */
.process-list {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: var(--space-8);
  counter-reset: step;
}
.process-step {
  position: relative;
  padding-top: var(--space-6);
}
.process-line-track {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 3px;
  background: var(--color-border);
  overflow: hidden;
}
.process-line-fill {
  display: block;
  width: 0;
  height: 100%;
  background: var(--gradient-accent);
}
.process-num {
  display: block;
  font-size: var(--text-sm);
  font-weight: 700;
  color: var(--color-accent);
  margin-bottom: var(--space-3);
  letter-spacing: 0.05em;
}
.process-step h3 { font-size: var(--text-lg); margin-bottom: var(--space-2); }
.process-step p { color: var(--color-muted); margin: 0; }

@media (max-width: 860px) {
  .process-list { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 560px) {
  .process-list { grid-template-columns: 1fr; }
}

/* ============================================
   Why us
   ============================================ */
.why-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-16);
  align-items: start;
}
.why-copy h2 { font-size: var(--text-4xl); margin-bottom: var(--space-5); }
.why-copy p { color: var(--color-muted); font-size: var(--text-lg); margin-bottom: var(--space-8); }

.why-cards {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  perspective: 1200px;
}
.why-card {
  display: flex;
  gap: var(--space-4);
  align-items: flex-start;
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-5);
  transition: box-shadow var(--duration-base) var(--ease-out), border-color var(--duration-base) var(--ease-out);
  will-change: transform;
}
.why-card:hover {
  box-shadow: 0 16px 36px -14px rgba(79, 91, 238, 0.3);
  border-color: transparent;
}
.why-card svg { color: var(--color-accent); flex-shrink: 0; margin-top: 2px; }
.why-card h3 { font-size: var(--text-base); margin-bottom: var(--space-1); }
.why-card p { color: var(--color-muted); margin: 0; font-size: var(--text-sm); }

@media (max-width: 860px) {
  .why-grid { grid-template-columns: 1fr; }
}

/* ============================================
   CTA band
   ============================================ */
.cta-band {
  background: var(--gradient-navy);
  color: #fff;
  text-align: center;
  padding-block: var(--space-20);
}
.cta-band h2 { font-size: var(--text-3xl); color: #fff; margin-bottom: var(--space-3); }
.cta-band p { color: #CBD5E1; font-size: var(--text-lg); margin-bottom: var(--space-8); }

/* ============================================
   Contact
   ============================================ */
.contact-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: var(--space-16);
}

.contact-info {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
  margin-block: var(--space-8);
}
.contact-info li {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  font-size: var(--text-base);
}
.contact-info svg { color: var(--color-accent); flex-shrink: 0; }
.contact-info a:hover { color: var(--color-accent); }

.contact-form {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-8);
  box-shadow: var(--shadow-sm);
}
.form-row { margin-bottom: var(--space-5); }
.form-row label {
  display: block;
  font-size: var(--text-sm);
  font-weight: 600;
  margin-bottom: var(--space-2);
}
.form-row input,
.form-row textarea {
  width: 100%;
  font: inherit;
  font-size: var(--text-base);
  padding: 0.8rem 1rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-background);
  color: var(--color-foreground);
  transition: border-color var(--duration-fast) var(--ease-out), box-shadow var(--duration-fast) var(--ease-out);
  resize: vertical;
}
.form-row input:focus,
.form-row textarea:focus {
  outline: none;
  border-color: var(--color-accent);
  box-shadow: 0 0 0 3px rgba(79, 91, 238, 0.15);
}
.form-row input[aria-invalid="true"],
.form-row textarea[aria-invalid="true"] {
  border-color: var(--color-destructive);
}
.field-error {
  display: block;
  min-height: 1.1em;
  color: var(--color-destructive);
  font-size: var(--text-xs);
  margin-top: var(--space-1);
}

.form-submit { width: 100%; }
.form-submit[disabled] { opacity: 0.7; cursor: not-allowed; }

.form-success[hidden] { display: none; }
.form-success {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-top: var(--space-4);
  padding: var(--space-3) var(--space-4);
  background: #ECFDF5;
  color: var(--color-success);
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  font-weight: 500;
}

@media (max-width: 860px) {
  .contact-grid { grid-template-columns: 1fr; }
}

/* ============================================
   Footer
   ============================================ */
.site-footer {
  background: var(--color-primary);
  color: #CBD5E1;
  padding-top: var(--space-16);
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  gap: var(--space-12);
  flex-wrap: wrap;
  padding-bottom: var(--space-12);
  border-bottom: 1px solid rgba(255,255,255,0.1);
}

.footer-brand { max-width: 320px; }
.footer-brand img { filter: brightness(0) invert(1); margin-bottom: var(--space-4); }
.footer-brand p { color: #94A3B8; font-size: var(--text-sm); }

.footer-nav { display: flex; gap: var(--space-16); }
.footer-nav h4 { color: #fff; font-size: var(--text-sm); margin-bottom: var(--space-4); }
.footer-nav ul { display: flex; flex-direction: column; gap: var(--space-3); }
.footer-nav a, .footer-nav li { color: #94A3B8; font-size: var(--text-sm); }
.footer-nav a:hover { color: #fff; }

.footer-bottom {
  padding-block: var(--space-6);
  font-size: var(--text-xs);
  color: #64748B;
}

@media (max-width: 640px) {
  .footer-inner { flex-direction: column; }
  .footer-nav { gap: var(--space-10); }
}

/* ============================================
   Scroll reveal
   ============================================ */
.reveal {
  opacity: 0;
  transform: translateY(16px);
  transition: opacity 600ms var(--ease-out), transform 600ms var(--ease-out);
}
.reveal.is-visible {
  opacity: 1;
  transform: translateY(0);
}
@media (prefers-reduced-motion: reduce) {
  .reveal { opacity: 1; transform: none; transition: none; }
}

/* Stagger-group children start hidden; GSAP ScrollTrigger animates them in
   with a per-item delay. Falls back to visible if GSAP never runs. */
.stagger-group > * {
  opacity: 0;
  transform: translateY(24px);
}
@media (prefers-reduced-motion: reduce) {
  .stagger-group > * { opacity: 1; transform: none; }
}

/* ============================================
   Back to top
   ============================================ */
.back-to-top {
  position: fixed;
  right: var(--space-6);
  bottom: var(--space-6);
  width: 48px;
  height: 48px;
  border: none;
  border-radius: var(--radius-full);
  background: var(--gradient-accent);
  color: #fff;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: var(--shadow-md);
  opacity: 0;
  visibility: hidden;
  transform: translateY(12px);
  transition: opacity var(--duration-base) var(--ease-out),
              transform var(--duration-base) var(--ease-out),
              visibility var(--duration-base);
  z-index: 90;
}
.back-to-top.is-visible {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
}
.back-to-top:hover { transform: translateY(-3px); }

@media (max-width: 640px) {
  .back-to-top { right: var(--space-4); bottom: var(--space-4); width: 44px; height: 44px; }
}