/*
  Sudipta Romen Biswas – personal site
  Modern dark-leaning design, responsive, with light/dark toggle.
*/

*, *::before, *::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

html {
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
  scroll-behavior: smooth;
}

body {
  min-height: 100vh;
  line-height: 1.6;
  font-family: var(--font-body, system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif);
  font-size: var(--text-base);
  background-color: var(--color-bg);
  color: var(--color-text);
}

img,
svg {
  display: block;
  max-width: 100%;
}

a {
  color: inherit;
  text-decoration: none;
}

a:hover {
  text-decoration: underline;
}

button {
  font: inherit;
  color: inherit;
  background: none;
  border: none;
  cursor: pointer;
}

:root {
  --font-body: 'Satoshi', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --font-display: 'Boska', 'Georgia', serif;

  --text-xs: 0.75rem;
  --text-sm: 0.875rem;
  --text-base: 1rem;
  --text-lg: 1.125rem;
  --text-xl: 1.5rem;
  --text-2xl: 2rem;
  --text-3xl: 2.5rem;

  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-6: 1.5rem;
  --space-8: 2rem;
  --space-12: 3rem;
  --space-16: 4rem;

  --radius-sm: 0.375rem;
  --radius-md: 0.5rem;
  --radius-lg: 0.75rem;
  --radius-full: 999px;

  --color-bg: #050609;
  --color-surface: #0b0d12;
  --color-surface-2: #151823;
  --color-surface-alt: #0f1119;
  --color-border: #242839;
  --color-text: #f3f4f8;
  --color-text-muted: #a0a3b5;
  --color-accent: #4fd1c5;
  --color-accent-soft: rgba(79, 209, 197, 0.12);
  --color-accent-strong: #2c7a7b;

  --shadow-soft: 0 18px 45px rgba(0, 0, 0, 0.55);

  --content-width: min(960px, 100% - 2.5rem);

  --transition-fast: 180ms ease-out;
}

html[data-theme='light'] {
  --color-bg: #f7f6f2;
  --color-surface: #ffffff;
  --color-surface-2: #f0f1f7;
  --color-surface-alt: #f3f4fb;
  --color-border: #d9dde9;
  --color-text: #12131a;
  --color-text-muted: #5b6178;
  --color-accent: #16a394;
  --color-accent-soft: rgba(22, 163, 148, 0.12);
  --color-accent-strong: #0f766e;

  --shadow-soft: 0 18px 45px rgba(15, 23, 42, 0.14);
}

.container {
  width: 100%;
  max-width: var(--content-width);
  margin-inline: auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 20;
  backdrop-filter: blur(18px);
  background: linear-gradient(to bottom, rgba(5, 6, 9, 0.9), rgba(5, 6, 9, 0.7));
  border-bottom: 1px solid rgba(15, 23, 42, 0.7);
}

html[data-theme='light'] .site-header {
  background: linear-gradient(to bottom, rgba(247, 246, 242, 0.95), rgba(247, 246, 242, 0.85));
  border-bottom-color: rgba(209, 213, 219, 0.9);
}

.header-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-4);
  padding-block: var(--space-3);
}

.brand {
  display: flex;
  align-items: center;
  gap: var(--space-3);
  text-decoration: none;
}

.brand-text {
  display: flex;
  flex-direction: column;
}

.brand-title {
  font-family: var(--font-display);
  font-size: var(--text-lg);
  letter-spacing: 0.03em;
}

.brand-subtitle {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

.logo-mark svg {
  width: 34px;
  height: 34px;
}

.logo-ring {
  fill: none;
  stroke: var(--color-accent);
  stroke-width: 1.4;
}

.logo-mark text {
  fill: var(--color-text);
  font-family: var(--font-body);
  font-size: 0.75rem;
  letter-spacing: 0.1em;
}

.site-nav {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  font-size: var(--text-sm);
}

.site-nav a {
  text-decoration: none;
  color: var(--color-text-muted);
  position: relative;
  padding-block: 0.15rem;
}

.site-nav a::after {
  content: '';
  position: absolute;
  left: 0;
  bottom: -0.25rem;
  width: 0;
  height: 2px;
  border-radius: 999px;
  background: linear-gradient(90deg, var(--color-accent), var(--color-accent-strong));
  transition: width var(--transition-fast);
}

.site-nav a:hover::after,
.site-nav a[aria-current='page']::after {
  width: 100%;
}

.site-nav a[aria-current='page'] {
  color: var(--color-text);
}

/* Anchor offset for fixed header */
section[id], h3[id], article[id] {
  scroll-margin-top: 100px; /* Precise pixel value for better control */
}

/* Nav dropdowns */
.nav-item {
  position: relative;
  /* Bridging the gap between nav-parent and dropdown */
  padding-bottom: 1rem;
  margin-bottom: -1rem;
}

.nav-parent {
  display: inline-flex;
  align-items: center;
  gap: 0.2rem;
}

.nav-chevron {
  transition: transform var(--transition-fast);
  flex-shrink: 0;
  pointer-events: none; /* Let clicks pass through to the link */
}

.nav-item:hover .nav-chevron,
.nav-item:focus-within .nav-chevron,
.nav-item.open .nav-chevron {
  transform: rotate(180deg);
}

.nav-dropdown {
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%) translateY(-8px);
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-2) 0;
  min-width: 15rem;
  opacity: 0;
  pointer-events: none;
  transition: opacity var(--transition-fast), transform var(--transition-fast);
  z-index: 200;
  box-shadow: var(--shadow-soft);
}

.nav-item:hover .nav-dropdown,
.nav-item:focus-within .nav-dropdown,
.nav-item.open .nav-dropdown {
  opacity: 1;
  pointer-events: auto;
  transform: translateX(-50%) translateY(0);
}

.nav-dropdown a {
  display: block;
  padding: var(--space-2) var(--space-4);
  color: var(--color-text-muted);
  font-size: var(--text-sm);
  white-space: nowrap;
}

.nav-dropdown a:hover {
  color: var(--color-accent);
  background: var(--color-accent-soft);
  text-decoration: none;
}

.nav-dropdown a::after {
  display: none;
}

.icon-button {
  width: 34px;
  height: 34px;
  border-radius: var(--radius-full);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  color: var(--color-text-muted);
  border: 1px solid rgba(148, 163, 184, 0.35);
  background: radial-gradient(circle at top left, rgba(148, 163, 184, 0.25), transparent 55%);
  transition: background var(--transition-fast), border-color var(--transition-fast), color var(--transition-fast), transform 150ms ease-out;
}

.icon-button:hover {
  border-color: var(--color-accent);
  color: var(--color-accent);
  transform: translateY(-1px);
}

.theme-toggle svg {
  width: 18px;
  height: 18px;
}

.nav-toggle {
  display: none;
  flex-direction: column;
  justify-content: center;
  gap: 4px;
  padding-inline: 0;
}

.nav-toggle span {
  width: 16px;
  height: 2px;
  border-radius: 999px;
  background: var(--color-text);
}

.hero {
  padding-block: var(--space-16) var(--space-12);
  background:
    radial-gradient(circle at top left, rgba(79, 209, 197, 0.22), transparent 55%),
    radial-gradient(circle at bottom right, rgba(59, 130, 246, 0.15), transparent 55%),
    linear-gradient(to bottom, var(--color-bg), var(--color-surface-alt));
}

.hero-compact {
  padding-block: var(--space-12) var(--space-8);
}

.hero-inner {
  display: flex;
  flex-direction: column;
  gap: var(--space-4);
}

.hero-text {
  max-width: 40rem;
}

.eyebrow {
  font-size: var(--text-sm);
  letter-spacing: 0.25em;
  text-transform: uppercase;
  color: var(--color-accent);
}

.hero-title {
  font-family: var(--font-display);
  font-size: clamp(2.4rem, 4vw, 3.2rem);
  line-height: 1.1;
  margin-top: var(--space-2);
}

.hero-tagline {
  margin-top: var(--space-3);
  font-size: var(--text-lg);
  color: var(--color-text-muted);
}

.hero-meta {
  margin-top: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

.section {
  padding-block: var(--space-12);
}

.section-alt {
  background: radial-gradient(circle at top right, rgba(148, 163, 184, 0.12), transparent 60%), var(--color-surface);
}

.split {
  display: grid;
  gap: var(--space-8);
}

.section-header h2 {
  font-family: var(--font-display);
  font-size: var(--text-2xl);
}

.section-header p {
  margin-top: var(--space-3);
  color: var(--color-text-muted);
}

.section-body p + p {
  margin-top: var(--space-3);
}

.section-body p {
  color: var(--color-text-muted);
}

.pill-list {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-4);
}

.pill {
  font-size: var(--text-xs);
  padding: 0.35rem 0.75rem;
  border-radius: var(--radius-full);
  border: 1px solid rgba(148, 163, 184, 0.4);
  background: radial-gradient(circle at top left, var(--color-accent-soft), transparent 65%);
}

.contact-block {
  text-align: left;
}

.contact-block h2 {
  font-family: var(--font-display);
  font-size: var(--text-xl);
  margin-bottom: var(--space-2);
}

.contact-block p {
  color: var(--color-text-muted);
}

.card-grid {
  display: grid;
  gap: var(--space-4);
}

.card {
  border-radius: var(--radius-lg);
  padding: var(--space-4);
  background: radial-gradient(circle at top left, rgba(79, 209, 197, 0.18), transparent 60%), var(--color-surface);
  border: 1px solid rgba(148, 163, 184, 0.45);
  box-shadow: var(--shadow-soft);
}

.card-muted {
  background: var(--color-surface-2);
}

.card-title {
  font-family: var(--font-display);
  font-size: var(--text-lg);
}

.card-body {
  margin-top: var(--space-2);
  color: var(--color-text-muted);
}

.card-img {
  width: 100%;
  margin-top: var(--space-3);
  border-radius: var(--radius-md);
  object-fit: cover;
}

.research-group-img {
  width: 100%;
  margin-top: var(--space-4);
  margin-bottom: var(--space-6);
  border-radius: var(--radius-md);
  object-fit: cover;
}

.card-list {
  margin-top: var(--space-2);
  padding: 0;
  list-style: none;
  color: var(--color-text-muted);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.card-list li {
  font-size: var(--text-sm);
  line-height: 1.5;
}

.card-meta {
  margin-top: var(--space-3);
  font-size: var(--text-xs);
  color: var(--color-text-muted);
}

.card-link {
  display: inline-flex;
  align-items: center;
  gap: 0.35rem;
  margin-top: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-accent);
  text-decoration: none;
}

.card-link::after {
  content: '">"';
  font-size: 0.85em;
}

.embed-wrapper {
  border-radius: var(--radius-lg);
  overflow: hidden;
  border: 1px solid rgba(148, 163, 184, 0.45);
  background: var(--color-surface-2);
  box-shadow: var(--shadow-soft);
}

.embed-wrapper iframe {
  width: 100%;
  min-height: 80vh;
  border: none;
  background: var(--color-bg);
}

.embed-note {
  margin-top: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

code {
  font-family: ui-monospace, SFMono-Regular, Menlo, Monaco, Consolas, 'Liberation Mono', 'Courier New', monospace;
  font-size: 0.85em;
  background: rgba(15, 23, 42, 0.6);
  padding: 0.15rem 0.4rem;
  border-radius: 0.25rem;
}

html[data-theme='light'] code {
  background: rgba(229, 231, 235, 0.9);
}

.site-footer {
  border-top: 1px solid rgba(15, 23, 42, 0.7);
  background: var(--color-surface);
}

html[data-theme='light'] .site-footer {
  border-top-color: rgba(209, 213, 219, 0.9);
}

.footer-inner {
  padding-block: var(--space-4);
  text-align: center;
  font-size: var(--text-sm);
  color: var(--color-text-muted);
}

@media (max-width: 768px) {
  .header-inner {
    align-items: center;
  }

  .site-nav {
    position: fixed;
    inset-inline: 0;
    top: 56px;
    padding: var(--space-4) var(--space-4) var(--space-6);
    background: var(--color-surface);
    flex-direction: column;
    align-items: flex-start;
    gap: var(--space-3);
    transform: translateY(-110%);
    opacity: 0;
    pointer-events: none;
    transition: transform var(--transition-fast), opacity var(--transition-fast);
  }

  .nav-item {
    width: 100%;
  }

  .nav-dropdown {
    position: static;
    transform: none;
    box-shadow: none;
    border: none;
    border-left: 2px solid var(--color-border);
    border-radius: 0;
    padding: var(--space-1) 0;
    margin-top: var(--space-1);
    margin-left: var(--space-4);
    background: transparent;
    min-width: 0;
    display: none;
    opacity: 1;
    pointer-events: auto;
  }

  .nav-item:hover .nav-dropdown,
  .nav-item:focus-within .nav-dropdown {
    transform: none;
  }

  .nav-item.open .nav-dropdown {
    display: flex;
    flex-direction: column;
    transform: none;
  }

  .site-header.nav-open .site-nav {
    transform: translateY(0);
    opacity: 1;
    pointer-events: auto;
  }

  .nav-toggle {
    display: inline-flex;
  }

  .site-header {
    background: linear-gradient(to bottom, rgba(5, 6, 9, 0.97), rgba(5, 6, 9, 0.94));
  }

  html[data-theme='light'] .site-header {
    background: linear-gradient(to bottom, rgba(247, 246, 242, 0.97), rgba(247, 246, 242, 0.94));
  }

  .hero {
    padding-block: var(--space-12) var(--space-10);
  }

  .split {
    grid-template-columns: 1fr;
  }
}

@media (min-width: 769px) {
  .split {
    grid-template-columns: minmax(0, 1.2fr) minmax(0, 1.8fr);
    align-items: flex-start;
  }

  .hero-inner {
    flex-direction: row;
    justify-content: space-between;
    align-items: flex-end;
  }

  .hero-text {
    max-width: 32rem;
  }

  .hero-with-photo {
    align-items: center;
  }

  .research-grid {
    grid-template-columns: repeat(2, 1fr);
  }

  /* certification-grid and portfolio-grid intentionally left single-column */
}

/* Hero with Photo */
.hero-with-photo {
  display: flex;
  flex-direction: column-reverse;
  gap: var(--space-8);
}

.hero-photo {
  flex-shrink: 0;
}

.profile-img {
  width: 180px;
  height: 180px;
  border-radius: 50%;
  object-fit: cover;
  border: 3px solid var(--color-accent);
  box-shadow: 0 0 40px rgba(79, 209, 197, 0.3);
}

@media (min-width: 769px) {
  .hero-with-photo {
    flex-direction: row;
  }

  .profile-img {
    width: 220px;
    height: 220px;
  }
}

/* Hero Links */
.hero-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-6);
}

.hero-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: 0.6rem 1rem;
  font-size: var(--text-sm);
  border-radius: var(--radius-full);
  border: 1px solid rgba(148, 163, 184, 0.4);
  background: radial-gradient(circle at top left, var(--color-accent-soft), transparent 65%);
  color: var(--color-text);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.hero-link:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
  text-decoration: none;
}

.hero-link svg {
  color: var(--color-accent);
}

.meta-highlight {
  color: var(--color-accent);
  font-weight: 500;
}

/* Section Header Full Width */
.section-header-full {
  margin-bottom: var(--space-8);
}

.section-header-full h2 {
  font-family: var(--font-display);
  font-size: var(--text-2xl);
}

.section-header-full p {
  margin-top: var(--space-3);
  color: var(--color-text-muted);
  max-width: 48rem;
}

.section-header-full .pill-list {
  margin-top: var(--space-4);
}

/* Research & Portfolio Grids */
.research-grid,
.portfolio-grid {
  display: grid;
  gap: var(--space-4);
}

.certification-grid {
  display: grid;
  gap: var(--space-4);
}

/* Card Enhancements */
.card-featured {
  border-color: rgba(79, 209, 197, 0.3);
}

.card-company {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  margin-bottom: var(--space-3);
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  font-weight: 500;
}

.company-logo {
  color: var(--color-accent);
  width: 1.45rem;
  height: 1.45rem;
  object-fit: contain;
  flex: 0 0 auto;
  display: block;
}

.company-logo-lumileds {
  width: 3rem;
  height: 3rem;
}

.company-text-logo {
  font-size: var(--text-lg);
  font-weight: 700;
  letter-spacing: 0.05em;
  color: var(--color-accent);
}

/* Section CTA */
.section-cta {
  margin-top: var(--space-8);
  text-align: center;
}

.cta-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: 0.75rem 1.5rem;
  font-size: var(--text-sm);
  font-weight: 500;
  color: var(--color-accent);
  border: 1px solid var(--color-accent);
  border-radius: var(--radius-full);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.cta-link:hover {
  background: var(--color-accent);
  color: var(--color-bg);
  text-decoration: none;
}

/* Contact Links */
.contact-links {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-4);
  margin-top: var(--space-6);
}

.contact-link {
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
  padding: 0.75rem 1.25rem;
  font-size: var(--text-sm);
  border-radius: var(--radius-full);
  border: 1px solid rgba(148, 163, 184, 0.4);
  background: var(--color-surface-2);
  color: var(--color-text);
  text-decoration: none;
  transition: all var(--transition-fast);
}

.contact-link:hover {
  border-color: var(--color-accent);
  transform: translateY(-2px);
  text-decoration: none;
}

.contact-link svg {
  color: var(--color-accent);
}

/* Contact Block Centered */
.contact-block {
  text-align: center;
  max-width: 600px;
  margin-inline: auto;
}

/* Strong text in muted paragraphs */
.section-body strong {
  color: var(--color-text);
}

/* Card link arrow fix */
.card-link::after {
  content: '→';
  font-size: 0.85em;
}

/* Multiple card links */
.card-links {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-top: var(--space-3);
}

.card-links .card-link {
  margin-top: 0;
  font-size: var(--text-xs);
  padding: 0.25rem 0.5rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-surface-2);
}

.card-links .card-link:hover {
  border-color: var(--color-accent);
}

/* Patent list styles */
.patent-list {
  margin-top: var(--space-4);
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.patent-item {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  flex-wrap: wrap;
  font-size: var(--text-sm);
}

.patent-status {
  font-size: var(--text-xs);
  font-weight: 600;
  padding: 0.15rem 0.5rem;
  border-radius: var(--radius-sm);
  text-transform: uppercase;
  letter-spacing: 0.02em;
}

.patent-status.granted {
  background: var(--color-success, #22c55e);
  color: #fff;
}

.patent-status.pending {
  background: var(--color-warning, #f59e0b);
  color: #000;
}

.patent-item a {
  color: var(--color-accent);
  text-decoration: none;
  font-weight: 500;
}

.patent-item a:hover {
  text-decoration: underline;
}

.patent-id {
  font-size: var(--text-xs);
  color: var(--color-text-muted);
  font-family: var(--font-mono, monospace);
}

/* Research Group Titles */
.research-group-title {
  font-family: var(--font-display);
  font-size: var(--text-xl);
  margin-top: var(--space-8);
  margin-bottom: var(--space-2);
  color: var(--color-accent);
}

.research-group-desc {
  font-size: var(--text-sm);
  color: var(--color-text-muted);
  margin-bottom: var(--space-4);
  max-width: 48rem;
}

.section-cta-group {
  margin-top: var(--space-8);
  text-align: center;
  padding-top: var(--space-4);
  border-top: 1px solid var(--color-border);
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: var(--space-4);
}