/* ==========================================================================
   Meghna Das — Portfolio
   Design tokens — purple palette, 3D depth theme
   ========================================================================== */

:root {
  /* Core palette (as specified) */
  --c1: #cfcfe8; /* lightest lavender */
  --c2: #a1a1ce; /* soft violet */
  --c3: #7474b0; /* mid violet */
  --c4: #4e4e94; /* strong violet */
  --c5: #313178; /* deepest indigo */
  --white: #ffffff;

  /* Roles */
  --color-bg: var(--c1);
  --color-bg-alt: #e3e3f2;
  --color-surface: rgba(255, 255, 255, 0.72);
  --color-surface-solid: var(--white);
  --color-ink: var(--c5);
  --color-ink-soft: var(--c4);
  --color-line: rgba(78, 78, 148, 0.22);
  --color-accent: var(--c4);
  --color-accent-dark: var(--c5);
  --color-accent-soft: var(--c2);

  /* Type */
  --font-display: "Space Grotesk", "Segoe UI", sans-serif;
  --font-body: "Source Serif 4", Georgia, serif;

  /* Layout */
  --max-width: 1180px;
  --gutter: clamp(1.5rem, 4vw, 3rem);
  --radius-sm: 8px;
  --radius-md: 16px;

  /* 3D shadow system — layered, purple-tinted */
  --shadow-card:
    0 1px 1px rgba(49, 49, 120, 0.10),
    0 8px 16px rgba(49, 49, 120, 0.12),
    0 24px 40px -12px rgba(49, 49, 120, 0.28);
  --shadow-card-hover:
    0 2px 4px rgba(49, 49, 120, 0.14),
    0 16px 28px rgba(49, 49, 120, 0.18),
    0 34px 60px -14px rgba(49, 49, 120, 0.38);
  --shadow-btn: 0 4px 0 var(--c5), 0 10px 18px rgba(49, 49, 120, 0.35);
  --shadow-btn-pressed: 0 1px 0 var(--c5), 0 4px 8px rgba(49, 49, 120, 0.3);

  /* Motion */
  --ease: cubic-bezier(0.22, 1, 0.36, 1);
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
    scroll-behavior: auto !important;
  }
}

/* ==========================================================================
   Reset
   ========================================================================== */

*, *::before, *::after { box-sizing: border-box; }

html {
  scroll-behavior: smooth;
  scroll-padding-top: 88px;
}

body {
  margin: 0;
  background: var(--color-bg);
  color: var(--color-ink);
  font-family: var(--font-body);
  font-size: 1.0625rem;
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

h1, h2, h3, h4 {
  font-family: var(--font-display);
  color: var(--color-ink);
  line-height: 1.15;
  margin: 0;
  font-weight: 600;
}

p { margin: 0 0 1em; }
ul, ol { margin: 0; padding: 0; list-style: none; }
a { color: inherit; text-decoration: none; }
img { max-width: 100%; display: block; }
button { font: inherit; cursor: pointer; }

.skip-link {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--c5);
  color: var(--c1);
  padding: 0.75rem 1.25rem;
  z-index: 1000;
  border-radius: 0 0 var(--radius-sm) 0;
}
.skip-link:focus { left: 0; }

:focus-visible {
  outline: 2px solid var(--c4);
  outline-offset: 3px;
}

/* ==========================================================================
   3D tilt-card base (JS adds the live rotation via CSS custom properties)
   ========================================================================== */

.tilt-card {
  --rx: 0deg;
  --ry: 0deg;
  --tz: 0px;
  transform-style: preserve-3d;
  transform: perspective(900px) rotateX(var(--rx)) rotateY(var(--ry)) translateZ(var(--tz));
  transition: transform 0.4s var(--ease), box-shadow 0.4s var(--ease), opacity 0.6s var(--ease);
  will-change: transform;
}

.tilt-card.reveal-pending { opacity: 0; transform: perspective(900px) translateY(18px); }
.tilt-card.reveal-visible { opacity: 1; }

/* ==========================================================================
   Layout helpers
   ========================================================================== */

.section-inner,
.header-inner,
.footer-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding-left: var(--gutter);
  padding-right: var(--gutter);
}

.section {
  padding: clamp(3.5rem, 8vw, 6.5rem) 0;
  position: relative;
}

.section-alt { background: var(--color-bg-alt); }

.section-heading-block {
  max-width: 46ch;
  margin-bottom: clamp(2rem, 5vw, 3.25rem);
}

.section-heading {
  font-size: clamp(1.75rem, 3vw, 2.25rem);
  margin-bottom: 0.5rem;
}

.section-lede {
  color: var(--color-ink-soft);
  font-size: 1.05rem;
  margin: 0;
}

/* ==========================================================================
   Buttons — beveled 3D style
   ========================================================================== */

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.5rem;
  font-family: var(--font-display);
  font-weight: 500;
  font-size: 0.95rem;
  padding: 0.85rem 1.6rem;
  border-radius: var(--radius-sm);
  border: 1px solid transparent;
  transition: transform 0.15s var(--ease), background 0.2s var(--ease), border-color 0.2s var(--ease), color 0.2s var(--ease), box-shadow 0.15s var(--ease);
}

.btn-primary {
  background: linear-gradient(180deg, var(--c4), var(--c5));
  color: var(--white);
  box-shadow: var(--shadow-btn);
}
.btn-primary:hover { transform: translateY(-2px); }
.btn-primary:active {
  transform: translateY(2px);
  box-shadow: var(--shadow-btn-pressed);
}

.btn-ghost {
  background: rgba(255, 255, 255, 0.5);
  border-color: var(--c4);
  color: var(--c5);
  backdrop-filter: blur(4px);
}
.btn-ghost:hover { background: var(--c4); color: var(--white); transform: translateY(-2px); }

.btn-small {
  padding: 0.55rem 1.1rem;
  font-size: 0.85rem;
  background: transparent;
  border-color: var(--c4);
  color: var(--c5);
  margin-top: 1.1rem;
  box-shadow: none;
}
.btn-small:hover { background: var(--c4); color: var(--white); }

.btn-full { width: 100%; }

/* ==========================================================================
   Header / Nav
   ========================================================================== */

.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(207, 207, 232, 0.82);
  backdrop-filter: blur(10px);
  border-bottom: 1px solid var(--color-line);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 72px;
}

.logo {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.1rem;
  letter-spacing: -0.01em;
  color: var(--c5);
}

.nav-list {
  display: flex;
  gap: clamp(1rem, 2vw, 1.75rem);
}

.nav-link {
  font-family: var(--font-display);
  font-size: 0.92rem;
  color: var(--color-ink-soft);
  position: relative;
  padding: 0.35rem 0.1rem;
  transition: color 0.2s var(--ease);
}

.nav-link::after {
  content: "";
  position: absolute;
  left: 0;
  bottom: -2px;
  width: 100%;
  height: 2px;
  background: var(--c4);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.25s var(--ease);
}

.nav-link:hover,
.nav-link.is-active { color: var(--c5); }
.nav-link.is-active::after { transform: scaleX(1); }

.nav-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  padding: 0.5rem;
}

.nav-toggle-bar {
  width: 22px;
  height: 2px;
  background: var(--c5);
  transition: transform 0.25s var(--ease), opacity 0.2s var(--ease);
}

.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(1) { transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(2) { opacity: 0; }
.nav-toggle[aria-expanded="true"] .nav-toggle-bar:nth-child(3) { transform: translateY(-7px) rotate(-45deg); }

/* ==========================================================================
   Hero
   ========================================================================== */

.hero {
  padding: clamp(3rem, 8vw, 5.5rem) 0 clamp(4rem, 10vw, 7rem);
  position: relative;
  overflow: hidden;
  background:
    radial-gradient(circle at 1px 1px, rgba(49, 49, 120, 0.10) 1px, transparent 0) 0 0/28px 28px,
    linear-gradient(180deg, var(--c1) 0%, var(--color-bg-alt) 100%);
}

.hero-bg {
  position: absolute;
  inset: 0;
  z-index: 0;
  background:
    radial-gradient(ellipse 55% 60% at 82% 18%, rgba(116, 116, 176, 0.35), transparent 70%),
    radial-gradient(ellipse 45% 50% at 8% 85%, rgba(78, 78, 148, 0.25), transparent 70%);
  pointer-events: none;
}

.hero-inner {
  position: relative;
  z-index: 1;
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 0 var(--gutter);
  display: grid;
  grid-template-columns: 1.1fr 0.9fr;
  gap: clamp(2rem, 5vw, 4rem);
  align-items: center;
}

.hero-eyebrow {
  font-family: var(--font-display);
  color: var(--c5);
  font-size: 0.95rem;
  margin-bottom: 1rem;
  opacity: 0;
  animation: rise 0.6s var(--ease) forwards;
}

.hero-heading {
  font-size: clamp(2.4rem, 5.5vw, 3.6rem);
  letter-spacing: -0.02em;
  margin-bottom: 0.9rem;
  opacity: 0;
  animation: rise 0.6s var(--ease) 0.08s forwards;
}

.hero-role {
  font-family: var(--font-display);
  font-size: clamp(1.05rem, 1.6vw, 1.25rem);
  color: var(--c5);
  margin-bottom: 1.1rem;
  opacity: 0;
  animation: rise 0.6s var(--ease) 0.16s forwards;
}

.hero-summary {
  color: var(--color-ink-soft);
  max-width: 52ch;
  font-size: 1.08rem;
  margin-bottom: 1.75rem;
  opacity: 0;
  animation: rise 0.6s var(--ease) 0.24s forwards;
}

.hero-actions {
  display: flex;
  gap: 1rem;
  flex-wrap: wrap;
  opacity: 0;
  animation: rise 0.6s var(--ease) 0.32s forwards;
}

@keyframes rise {
  from { opacity: 0; transform: translateY(14px); }
  to { opacity: 1; transform: translateY(0); }
}

/* ------------------------- Hero visual: 3D photo + chips ------------------------- */

.hero-visual {
  position: relative;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 420px;
  opacity: 0;
  animation: rise 0.7s var(--ease) 0.35s forwards;
}

.photo-frame {
  position: relative;
  width: min(320px, 78%);
  aspect-ratio: 4 / 5;
  border-radius: var(--radius-md);
  overflow: hidden;
  border: 6px solid var(--white);
  box-shadow: var(--shadow-card);
}

.photo-img {
  width: 100%;
  height: 100%;
  object-fit: cover;
  filter: saturate(0.92) contrast(1.02);
}

.photo-glow {
  position: absolute;
  inset: 0;
  background: linear-gradient(200deg, rgba(49, 49, 120, 0.05) 0%, rgba(49, 49, 120, 0.35) 100%);
  mix-blend-mode: multiply;
  pointer-events: none;
}

.floating-chip {
  position: absolute;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.15rem;
  background: rgba(255, 255, 255, 0.75);
  backdrop-filter: blur(10px);
  border: 1px solid rgba(255, 255, 255, 0.6);
  border-radius: 50%;
  width: 92px;
  height: 92px;
  box-shadow: var(--shadow-card);
}

.chip-value {
  font-family: var(--font-display);
  font-weight: 700;
  font-size: 1.25rem;
  color: var(--c5);
}

.chip-label {
  font-size: 0.68rem;
  color: var(--c4);
  text-align: center;
  line-height: 1.1;
}

.chip-cgpa { top: 4%; left: 0%; }
.chip-bi { bottom: 10%; left: -2%; }
.chip-seo { top: 40%; right: -4%; }

/* ==========================================================================
   About
   ========================================================================== */

.about-grid {
  display: grid;
  grid-template-columns: 0.8fr 1.2fr;
  gap: clamp(2rem, 5vw, 4rem);
}

.about-body p {
  color: var(--color-ink-soft);
  max-width: 60ch;
}

.stat-row {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.25rem;
  margin-top: 2rem;
  padding-top: 2rem;
  border-top: 1px solid var(--color-line);
}

.stat {
  display: flex;
  flex-direction: column;
  gap: 0.2rem;
  background: var(--color-surface);
  border: 1px solid rgba(255, 255, 255, 0.6);
  border-radius: var(--radius-sm);
  padding: 1rem 1.1rem;
  box-shadow: var(--shadow-card);
}

.stat-value {
  font-family: var(--font-display);
  font-size: 1.6rem;
  font-weight: 700;
  color: var(--c5);
}

.stat-label { font-size: 0.85rem; color: var(--color-ink-soft); }

/* ==========================================================================
   Skills
   ========================================================================== */

.skills-grid {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 1.25rem;
}

.skill-card {
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  padding: 1.6rem 1.5rem;
  box-shadow: var(--shadow-card);
}

.skill-card:hover { box-shadow: var(--shadow-card-hover); }

.skill-card-title {
  font-size: 1.05rem;
  margin-bottom: 1rem;
  padding-bottom: 0.75rem;
  border-bottom: 2px solid var(--c2);
}

.tag-list li {
  display: inline-block;
  font-size: 0.85rem;
  color: var(--c5);
  background: var(--c1);
  border: 1px solid rgba(78, 78, 148, 0.25);
  border-radius: 999px;
  padding: 0.35rem 0.8rem;
  margin: 0 0.4rem 0.4rem 0;
}

/* ==========================================================================
   Education timeline
   ========================================================================== */

.timeline {
  position: relative;
  max-width: 760px;
  padding-left: 2rem;
}

.timeline::before {
  content: "";
  position: absolute;
  left: 5px;
  top: 6px;
  bottom: 6px;
  width: 2px;
  background: var(--c2);
}

.timeline-item { position: relative; padding-bottom: 2.25rem; }
.timeline-item:last-child { padding-bottom: 0; }

.timeline-dot {
  position: absolute;
  left: -2rem;
  top: 4px;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--c4);
  border: 2px solid var(--color-bg);
  box-shadow: 0 0 0 2px var(--c4);
}

.timeline-content {
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  padding: 1.4rem 1.6rem;
  box-shadow: var(--shadow-card);
}

.timeline-year {
  font-family: var(--font-display);
  font-size: 0.85rem;
  color: var(--c4);
  margin-bottom: 0.3rem;
}

.timeline-title { font-size: 1.15rem; margin-bottom: 0.3rem; }
.timeline-org { color: var(--color-ink-soft); margin-bottom: 0.2rem; }
.timeline-meta { font-size: 0.9rem; color: var(--color-ink-soft); margin: 0; }

/* ==========================================================================
   Projects
   ========================================================================== */

.filter-bar {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-bottom: 2.25rem;
}

.filter-btn {
  font-family: var(--font-display);
  font-size: 0.85rem;
  background: rgba(255, 255, 255, 0.5);
  border: 1px solid var(--color-line);
  color: var(--color-ink-soft);
  padding: 0.5rem 1.05rem;
  border-radius: 999px;
  transition: background 0.2s var(--ease), color 0.2s var(--ease), border-color 0.2s var(--ease);
}

.filter-btn:hover { border-color: var(--c4); color: var(--c5); }

.filter-btn.is-active {
  background: linear-gradient(180deg, var(--c4), var(--c5));
  border-color: var(--c5);
  color: var(--white);
}

.project-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1.75rem;
}

.project-card {
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  overflow: hidden;
  display: flex;
  flex-direction: column;
  box-shadow: var(--shadow-card);
}

.project-card:hover { box-shadow: var(--shadow-card-hover); }

.project-card.is-hidden { display: none; }

.project-media {
  height: 170px;
  background-size: cover;
  background-position: center;
  position: relative;
}

.project-media::after {
  content: "";
  position: absolute;
  inset: 0;
  background: linear-gradient(180deg, rgba(49, 49, 120, 0.15) 0%, rgba(49, 49, 120, 0.75) 100%);
}

.project-media-tag {
  position: absolute;
  left: 1rem;
  bottom: 0.85rem;
  z-index: 1;
  font-family: var(--font-display);
  font-size: 0.75rem;
  color: var(--white);
  background: rgba(49, 49, 120, 0.55);
  border: 1px solid rgba(255, 255, 255, 0.4);
  padding: 0.3rem 0.75rem;
  border-radius: 999px;
  backdrop-filter: blur(4px);
}

.project-body {
  padding: 1.6rem 1.65rem 1.75rem;
  display: flex;
  flex-direction: column;
  flex-grow: 1;
}

.project-card-head { margin-bottom: 0.6rem; }

.project-title { font-size: 1.12rem; margin-bottom: 0.35rem; }

.project-org {
  color: var(--c4);
  font-family: var(--font-display);
  font-size: 0.88rem;
  margin: 0;
}

.project-role {
  font-size: 0.88rem;
  font-weight: 600;
  color: var(--color-ink-soft);
  margin-bottom: 0.6rem;
  font-family: var(--font-display);
}

.project-desc {
  color: var(--color-ink-soft);
  font-size: 0.98rem;
  flex-grow: 1;
}

.tag-list-compact { margin-top: auto; }
.tag-list-compact li { font-size: 0.78rem; padding: 0.3rem 0.65rem; }

.filter-empty { text-align: center; color: var(--color-ink-soft); padding: 2rem 0; }

/* ==========================================================================
   Experience
   ========================================================================== */

.experience-card {
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-left: 5px solid var(--c4);
  border-radius: var(--radius-md);
  padding: 2rem;
  max-width: 760px;
  box-shadow: var(--shadow-card);
}

.experience-head { margin-bottom: 0.75rem; }
.experience-role { font-size: 1.25rem; margin-bottom: 0.2rem; }
.experience-org { font-family: var(--font-display); color: var(--c4); margin: 0; }
.experience-desc { color: var(--color-ink-soft); }

.responsibility-list { display: grid; gap: 0.6rem; }

.responsibility-list li {
  position: relative;
  padding-left: 1.4rem;
  color: var(--color-ink-soft);
}

.responsibility-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.55em;
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--c3);
}

/* ==========================================================================
   Certification
   ========================================================================== */

.cert-card {
  display: flex;
  gap: 1.5rem;
  align-items: flex-start;
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  padding: 2rem;
  max-width: 760px;
  box-shadow: var(--shadow-card);
}

.cert-icon { flex-shrink: 0; width: 48px; height: 48px; color: var(--c4); }

.cert-icon svg {
  width: 100%;
  height: 100%;
  fill: none;
  stroke: currentColor;
  stroke-width: 2.5;
  stroke-linejoin: round;
  stroke-linecap: round;
}

.cert-title { font-size: 1.1rem; margin-bottom: 0.35rem; }
.cert-org { font-family: var(--font-display); color: var(--c4); margin-bottom: 0.35rem; }
.cert-meta { color: var(--color-ink-soft); font-size: 0.9rem; margin: 0; }

/* ==========================================================================
   Contact
   ========================================================================== */

.contact-grid {
  display: grid;
  grid-template-columns: 0.9fr 1.1fr;
  gap: clamp(2rem, 5vw, 4rem);
  align-items: start;
}

.contact-list { margin-top: 1.75rem; display: grid; gap: 1.1rem; }

.contact-list li {
  display: flex;
  flex-direction: column;
  gap: 0.15rem;
  border-bottom: 1px solid var(--color-line);
  padding-bottom: 0.75rem;
}

.contact-label { font-family: var(--font-display); font-size: 0.8rem; color: var(--color-ink-soft); }
.contact-value { font-size: 1.02rem; transition: color 0.2s var(--ease); }
a.contact-value:hover { color: var(--c5); }

.social-row {
  display: flex;
  gap: 0.9rem;
  margin-top: 1.75rem;
}

.social-icon {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--color-surface-solid);
  color: var(--c4);
  border: 1px solid var(--color-line);
  box-shadow: var(--shadow-card);
  transition: transform 0.2s var(--ease), color 0.2s var(--ease), background 0.2s var(--ease);
}

.social-icon svg { width: 20px; height: 20px; fill: currentColor; }

.social-icon:hover {
  background: linear-gradient(180deg, var(--c4), var(--c5));
  color: var(--white);
  transform: translateY(-3px);
}

.social-row-footer .social-icon {
  width: 38px;
  height: 38px;
  box-shadow: none;
  background: rgba(255, 255, 255, 0.08);
  border-color: rgba(255, 255, 255, 0.18);
  color: var(--c1);
}

.social-row-footer .social-icon svg { width: 17px; height: 17px; }

.social-row-footer .social-icon:hover { background: var(--c2); color: var(--c5); }

.contact-form {
  background: var(--color-surface-solid);
  border: 1px solid var(--color-line);
  border-radius: var(--radius-md);
  padding: 2rem;
  display: grid;
  gap: 1.25rem;
  box-shadow: var(--shadow-card);
}

.form-field { display: grid; gap: 0.4rem; }

.form-field label { font-family: var(--font-display); font-size: 0.88rem; color: var(--color-ink-soft); }

.form-field input,
.form-field textarea {
  font: inherit;
  font-size: 0.98rem;
  padding: 0.75rem 0.9rem;
  border: 1px solid var(--color-line);
  border-radius: var(--radius-sm);
  background: var(--c1);
  color: var(--c5);
  resize: vertical;
  transition: border-color 0.2s var(--ease);
}

.form-field input:focus,
.form-field textarea:focus { border-color: var(--c4); }

.form-field.has-error input,
.form-field.has-error textarea { border-color: #B23B3B; }

.form-error { font-size: 0.8rem; color: #B23B3B; min-height: 1em; }

.form-status { margin: 0; font-size: 0.92rem; color: var(--c5); min-height: 1.2em; }

/* ==========================================================================
   Footer / Back to top
   ========================================================================== */

.site-footer {
  background: linear-gradient(180deg, var(--c5), #262260);
  color: var(--c1);
  padding: 2.25rem 0;
}

.footer-inner {
  display: flex;
  justify-content: space-between;
  align-items: center;
  flex-wrap: wrap;
  gap: 1rem;
  font-size: 0.9rem;
}

.footer-inner p { margin: 0; }

.footer-email { color: var(--c2); transition: color 0.2s var(--ease); }
.footer-email:hover { color: var(--white); }

.back-to-top {
  position: fixed;
  right: 1.5rem;
  bottom: 1.5rem;
  width: 46px;
  height: 46px;
  border-radius: 50%;
  border: none;
  background: linear-gradient(180deg, var(--c4), var(--c5));
  color: var(--white);
  display: flex;
  align-items: center;
  justify-content: center;
  opacity: 0;
  visibility: hidden;
  transform: translateY(8px);
  transition: opacity 0.25s var(--ease), transform 0.25s var(--ease), visibility 0.25s;
  box-shadow: var(--shadow-card);
  z-index: 90;
}

.back-to-top.is-visible { opacity: 1; visibility: visible; transform: translateY(0); }
.back-to-top:hover { transform: translateY(-3px); }
.back-to-top svg { width: 18px; height: 18px; fill: currentColor; }

/* ==========================================================================
   Responsive
   ========================================================================== */

@media (max-width: 960px) {
  .hero-inner { grid-template-columns: 1fr; }
  .hero-visual { min-height: 340px; }
  .about-grid,
  .contact-grid { grid-template-columns: 1fr; }
  .skills-grid { grid-template-columns: repeat(2, 1fr); }
  .project-grid { grid-template-columns: 1fr; }
  .stat-row { grid-template-columns: repeat(2, 1fr); row-gap: 1.5rem; }
}

@media (max-width: 720px) {
  :root { --gutter: 1.25rem; }

  .main-nav {
    position: fixed;
    inset: 72px 0 0 0;
    background: var(--color-bg);
    padding: 1.5rem var(--gutter);
    transform: translateY(-8px);
    opacity: 0;
    visibility: hidden;
    transition: opacity 0.25s var(--ease), transform 0.25s var(--ease), visibility 0.25s;
  }

  .main-nav.is-open { opacity: 1; visibility: visible; transform: translateY(0); }

  .nav-list { flex-direction: column; gap: 0.25rem; }

  .nav-list a {
    display: block;
    padding: 0.9rem 0;
    font-size: 1.05rem;
    border-bottom: 1px solid var(--color-line);
  }

  .nav-toggle { display: flex; }

  .tilt-card { transform: none !important; }

  .hero-actions { gap: 0.75rem; }
  .btn { padding: 0.8rem 1.15rem; }
  .timeline-content,
  .experience-card,
  .cert-card,
  .contact-form { padding: 1.35rem; }
  .contact-value { overflow-wrap: anywhere; }
}

@media (max-width: 560px) {
  body { font-size: 1rem; }

  .section { padding: 3.5rem 0; }
  .section-heading-block { margin-bottom: 1.75rem; }

  .header-inner { height: 64px; }
  .main-nav { inset: 64px 0 0 0; }
  .logo { font-size: 1rem; }

  .hero { padding-top: 2.5rem; }
  .hero-heading { font-size: clamp(2.1rem, 11vw, 3rem); }
  .hero-summary { font-size: 1rem; }
  .hero-actions { flex-direction: column; align-items: stretch; }
  .hero-actions .btn { width: 100%; }

  .skills-grid { grid-template-columns: 1fr; }
  .cert-card { flex-direction: column; }
  .photo-frame { transform: none; }
  .hero-visual { display: grid; grid-template-columns: repeat(3, 1fr); gap: 0.5rem; min-height: auto; }
  .photo-frame { grid-column: 1 / -1; justify-self: center; width: min(280px, 82vw); }
  .floating-chip { position: static; width: 76px; height: 76px; justify-self: center; }
  .chip-value { font-size: 1rem; }
  .chip-label { font-size: 0.6rem; }

  .stat-row { gap: 0.75rem; }
  .stat { padding: 0.85rem; }
  .stat-value { font-size: 1.35rem; }
  .stat-label { font-size: 0.78rem; }

  .timeline { padding-left: 1.5rem; }
  .timeline-dot { left: -1.5rem; }
  .timeline-content { padding: 1.15rem; }
  .timeline-title { font-size: 1.05rem; }

  .filter-bar { gap: 0.45rem; }
  .filter-btn { padding: 0.45rem 0.75rem; }
  .project-body { padding: 1.25rem; }

  .footer-inner { align-items: flex-start; flex-direction: column; }
}