:root {
  --bg: #ffffff;
  --bg-soft: #f8f9fa;
  --paper: #ffffff;
  --ink: #1a1a1a;
  --muted: #666666;
  --line: #e5e7eb;
  --strong-line: #e5e7eb;
  --brand: #000000;
  --brand-soft: rgba(0, 0, 0, 0.08);
  --brand-gradient: #000000;
  --nav-glass: rgba(255, 255, 255, 0.95);
  --card-shadow: 0 4px 15px rgba(0, 0, 0, 0.05);
}

html.dark-mode {
  --bg: #111111;
  --bg-soft: #181818;
  --paper: #1f1f1f;
  --ink: #ffffff;
  --muted: #a0a0a0;
  --line: #333333;
  --strong-line: #333333;
  --brand: #ffffff;
  --brand-soft: rgba(255, 255, 255, 0.1);
  --brand-gradient: #ffffff;
  --nav-glass: rgba(17, 17, 17, 0.95);
  --card-shadow: 0 4px 15px rgba(255, 255, 255, 0.05);
}

* {
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
  scroll-padding-top: 82px;
}

body {
  min-height: 100vh;
  margin: 0;
  padding-top: 72px;
  overflow-x: hidden;
  background: var(--bg);
  color: var(--ink);
  font-family: "Poppins", sans-serif;
  transition: background-color 0.25s ease, color 0.25s ease;
}

a,
button {
  font-family: inherit;
}

button {
  appearance: none;
}

::selection {
  background: var(--brand);
  color: #ffffff;
}

/* Navigation */
.navbar {
  top: 0;
  min-height: 72px;
  padding: 0;
  border-bottom: 1px solid transparent;
  background: var(--nav-glass) !important;
  box-shadow: none;
  backdrop-filter: blur(16px);
  transition: border-color 0.25s ease;
}

.navbar.is-scrolled {
  border-bottom-color: var(--line);
}

.navbar .container-fluid {
  width: min(100%, 1080px);
  min-height: 71px;
  margin: 0 auto;
  padding-inline: 20px;
}

.navbar-brand {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  margin: 0;
  padding: 0;
  color: var(--ink) !important;
  font-size: 0.95rem;
  font-weight: 700;
}

.brand-mark {
  width: 32px;
  height: 32px;
  display: inline-flex;
  flex: 0 0 32px;
  align-items: center;
  justify-content: center;
  border-radius: 9px;
  background: var(--brand);
  color: #ffffff;
  font-size: 0.75rem;
}

.navbar-nav .nav-link {
  margin: 0;
  padding: 9px 12px !important;
  border-radius: 9px;
  color: var(--muted) !important;
  font-size: 0.8rem;
  font-weight: 600;
  transition: color 0.2s ease, background-color 0.2s ease;
}

.navbar-nav .nav-link:hover,
.navbar-nav .nav-link.active {
  background: var(--bg-soft);
  color: var(--ink) !important;
}

.btn-theme,
.navbar-toggler {
  width: 36px;
  height: 36px;
  padding: 0;
  border: 0;
  border-radius: 9px;
  background: var(--bg-soft);
  color: var(--ink);
  box-shadow: none;
  font-size: 0.8rem;
}

.btn-theme {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
}

.btn-theme:hover {
  color: var(--brand);
}

.btn-theme:focus-visible,
.nav-link:focus-visible,
.navbar-brand:focus-visible,
.navbar-toggler:focus-visible,
.learning-card:focus-visible,
#back-to-top:focus-visible {
  outline: 2px solid var(--brand);
  outline-offset: 3px;
}

/* Personal page intro */
.page-intro {
  width: min(calc(100% - 40px), 1080px);
  margin: 0 auto;
  padding: 56px 0 34px;
  border-bottom: 1px solid var(--line);
}

.breadcrumb-nav {
  display: flex;
  align-items: center;
  gap: 9px;
  margin-bottom: 38px;
  color: var(--muted);
  font-size: 0.7rem;
  font-weight: 600;
}

.breadcrumb-nav a {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  color: var(--muted);
  text-decoration: none;
}

.breadcrumb-nav a:hover {
  color: var(--brand);
}

.intro-copy {
  max-width: 720px;
}

.section-eyebrow {
  display: block;
  margin-bottom: 12px;
  color: var(--brand);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.08em;
  text-transform: uppercase;
}

.intro-copy h1 {
  margin: 0 0 17px;
  color: var(--ink);
  font-family: "Montserrat", sans-serif;
  font-size: clamp(2.45rem, 6vw, 4.6rem);
  font-weight: 700;
  letter-spacing: -0.055em;
  line-height: 0.98;
}

.intro-copy p {
  max-width: 620px;
  margin: 0;
  color: var(--muted);
  font-size: 0.9rem;
  line-height: 1.75;
}

/* Learning cards */
main.container {
  max-width: 1080px;
  padding: 48px 0 80px;
}

.library-heading {
  display: flex;
  align-items: end;
  justify-content: space-between;
  gap: 24px;
  margin-bottom: 22px;
}

.library-heading h2 {
  margin: 0;
  color: var(--ink);
  font-family: "Montserrat", sans-serif;
  font-size: 1.55rem;
  font-weight: 700;
  letter-spacing: -0.025em;
}

.library-heading p {
  max-width: 355px;
  margin: 0;
  color: var(--muted);
  font-size: 0.7rem;
  line-height: 1.6;
}

.learning-grid {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 14px;
}

.learning-card {
  position: relative;
  width: 100%;
  aspect-ratio: 3 / 4;
  min-height: 0;
  display: block;
  padding: 0;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: 18px;
  background: #111111;
  color: #ffffff;
  text-decoration: none;
  text-align: left;
  cursor: pointer;
  isolation: isolate;
  animation: card-enter 0.55s cubic-bezier(0.22, 1, 0.36, 1) both;
  transition:
    border-color 0.3s ease,
    box-shadow 0.35s ease,
    transform 0.35s cubic-bezier(0.22, 1, 0.36, 1);
}

.learning-card:nth-child(2) {
  animation-delay: 0.06s;
}

.learning-card:nth-child(3) {
  animation-delay: 0.12s;
}

.learning-card:nth-child(4) {
  animation-delay: 0.18s;
}

.learning-card:nth-child(5) {
  animation-delay: 0.24s;
}

.learning-card:nth-child(6) {
  animation-delay: 0.3s;
}

.learning-card-image,
.learning-card-shade {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
}

.learning-card-image {
  z-index: -2;
  display: block;
  object-fit: cover;
  object-position: center top;
  filter: saturate(0.88) contrast(1.03);
  transform: scale(1.002);
  transition:
    filter 0.6s ease,
    transform 0.75s cubic-bezier(0.22, 1, 0.36, 1);
}

.learning-card-shade {
  z-index: -1;
  background:
    linear-gradient(180deg, rgba(0, 0, 0, 0.1) 8%, transparent 36%),
    linear-gradient(0deg, rgba(5, 8, 12, 0.96) 0%, rgba(5, 8, 12, 0.7) 29%, transparent 68%);
  transition: opacity 0.4s ease;
}

.learning-card::after {
  content: "";
  position: absolute;
  top: -35%;
  left: -85%;
  width: 38%;
  height: 170%;
  z-index: 3;
  background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
  opacity: 0;
  pointer-events: none;
  transform: rotate(17deg);
}

.learning-card-top {
  position: absolute;
  top: 15px;
  right: 15px;
  left: 15px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
}

.learning-card-topic,
.learning-card-number {
  min-height: 30px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid rgba(255, 255, 255, 0.2);
  background: rgba(12, 15, 19, 0.54);
  color: rgba(255, 255, 255, 0.92);
  backdrop-filter: blur(10px);
}

.learning-card-topic {
  gap: 7px;
  padding: 0 10px;
  border-radius: 999px;
  font-size: 0.62rem;
  font-weight: 700;
}

.learning-card-topic i {
  color: #4facfe;
}

.learning-card-number {
  width: 30px;
  border-radius: 9px;
  font-family: "Montserrat", sans-serif;
  font-size: 0.62rem;
  font-weight: 700;
}

.learning-card-body {
  position: absolute;
  right: 18px;
  bottom: 18px;
  left: 18px;
  display: flex;
  flex-direction: column;
  align-items: flex-start;
  transform: translateY(42px);
  transition: transform 0.45s cubic-bezier(0.22, 1, 0.36, 1);
}

.learning-card-state {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  margin-bottom: 8px;
  color: rgba(255, 255, 255, 0.68);
  font-size: 0.58rem;
  font-weight: 700;
  letter-spacing: 0.05em;
  text-transform: uppercase;
}

.learning-card-state.is-ready {
  color: #4facfe;
}

.learning-card-body strong {
  display: block;
  color: #ffffff;
  font-family: "Montserrat", sans-serif;
  font-size: clamp(1.35rem, 2.2vw, 1.75rem);
  font-weight: 700;
  letter-spacing: -0.025em;
  line-height: 1.08;
}

.learning-card-description {
  max-width: 96%;
  display: block;
  margin-top: 8px;
  color: rgba(255, 255, 255, 0.74);
  font-size: 0.68rem;
  line-height: 1.55;
}

.learning-card-action {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 10px;
  margin-top: 14px;
  padding-top: 12px;
  border-top: 1px solid rgba(255, 255, 255, 0.18);
  color: #ffffff;
  font-size: 0.68rem;
  font-weight: 700;
  opacity: 0;
  transform: translateY(8px);
  transition: opacity 0.3s ease, transform 0.35s ease;
}

.learning-card-action.is-muted {
  color: rgba(255, 255, 255, 0.58);
}

.learning-card:hover {
  border-color: color-mix(in srgb, var(--brand) 65%, transparent);
  box-shadow: var(--card-shadow);
  transform: translateY(-8px);
}

.learning-card:hover .learning-card-image {
  filter: saturate(1.08) contrast(1.05);
  transform: scale(1.07);
}

.learning-card:hover .learning-card-body,
.learning-card:focus-visible .learning-card-body {
  transform: translateY(0);
}

.learning-card:hover .learning-card-action,
.learning-card:focus-visible .learning-card-action {
  opacity: 1;
  transform: translateY(0);
}

.learning-card:hover::after {
  opacity: 1;
  animation: card-shine 0.85s ease forwards;
}

.personal-note {
  display: flex;
  align-items: flex-start;
  gap: 11px;
  margin-top: 26px;
  padding: 15px 17px;
  border: 1px solid var(--line);
  border-radius: 13px;
  background: var(--bg-soft);
  color: var(--muted);
}

.personal-note i {
  margin-top: 3px;
  color: var(--brand);
}

.personal-note p {
  margin: 0;
  font-size: 0.7rem;
  line-height: 1.65;
}

@keyframes card-enter {
  from {
    opacity: 0;
    transform: translateY(18px);
  }

  to {
    opacity: 1;
    transform: translateY(0);
  }
}

@keyframes card-shine {
  from {
    left: -85%;
  }

  to {
    left: 150%;
  }
}

/* Footer */
footer {
  padding: 38px 20px 26px;
  border-top: 1px solid var(--line);
  background: var(--paper);
}

.footer-inner {
  width: min(100%, 1080px);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 20px;
  margin: 0 auto 22px;
}

.footer-brand {
  display: inline-flex;
  align-items: center;
  gap: 11px;
  color: var(--ink) !important;
  text-decoration: none !important;
}

.footer-brand > span:last-child {
  display: flex;
  flex-direction: column;
  gap: 3px;
}

.footer-brand strong {
  font-size: 0.82rem;
}

.footer-brand small {
  color: var(--muted);
  font-size: 0.62rem;
}

.social-icons {
  display: flex;
  gap: 8px;
}

.social-link {
  width: 38px;
  height: 38px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--line);
  border-radius: 9px;
  background: var(--paper);
  color: var(--ink);
  text-decoration: none !important;
}

.social-link:hover {
  background: var(--bg-soft);
  color: var(--brand);
}

.copyright {
  width: min(100%, 1080px);
  margin: 0 auto;
  padding-top: 20px;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: 0.64rem;
  text-align: center;
}

#back-to-top {
  position: fixed;
  right: 22px;
  bottom: 22px;
  z-index: 20;
  width: 38px;
  height: 38px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--paper);
  color: var(--ink);
  opacity: 0;
  pointer-events: none;
  transform: translateY(8px);
  transition: opacity 0.2s ease, transform 0.2s ease;
}

#back-to-top.is-visible {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

.app-toast {
  position: fixed;
  left: 50%;
  bottom: 24px;
  z-index: 30;
  max-width: calc(100% - 32px);
  padding: 11px 15px;
  border-radius: 12px;
  background: var(--ink);
  color: var(--paper);
  font-size: 0.72rem;
  font-weight: 600;
  opacity: 0;
  pointer-events: none;
  transform: translate(-50%, 12px);
  transition: opacity 0.2s ease, transform 0.2s ease;
}

.app-toast.is-visible {
  opacity: 1;
  transform: translate(-50%, 0);
}

@media (max-width: 1120px) {
  main.container {
    padding-inline: 20px;
  }
}

@media (max-width: 900px) {
  .learning-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (max-width: 768px) {
  body {
    padding-top: 60px;
  }

  .navbar,
  .navbar .container-fluid {
    min-height: 60px;
  }

  .navbar .container-fluid {
    padding-inline: 14px;
  }

  .navbar-brand {
    font-size: 0.9rem;
  }

  .brand-mark {
    width: 30px;
    height: 30px;
    flex-basis: 30px;
  }

  .btn-theme,
  .navbar-toggler {
    width: 40px;
    height: 40px;
  }

  .navbar-collapse {
    position: absolute;
    top: calc(100% + 8px);
    right: 14px;
    width: 210px;
    padding: 8px;
    border: 1px solid var(--line);
    border-radius: 14px;
    background: var(--paper);
    box-shadow: var(--card-shadow);
  }

  .navbar-nav {
    align-items: stretch !important;
  }

  .page-intro {
    width: calc(100% - 32px);
    padding: 34px 0 28px;
  }

  .breadcrumb-nav {
    margin-bottom: 28px;
  }

  .intro-copy h1 {
    font-size: 2.7rem;
  }

  main.container {
    padding: 38px 16px 58px;
  }

  .library-heading {
    display: block;
  }

  .library-heading p {
    margin-top: 10px;
  }
}

@media (max-width: 560px) {
  .learning-grid {
    grid-template-columns: 1fr;
  }

  .learning-card {
    max-height: 560px;
  }

  .learning-card-body {
    transform: translateY(0);
  }

  .learning-card-action {
    opacity: 1;
    transform: translateY(0);
  }

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

@media (max-width: 420px) {
  .intro-copy h1 {
    font-size: 2.35rem;
  }

  .intro-copy p {
    font-size: 0.82rem;
  }

  .learning-card-body {
    right: 16px;
    bottom: 16px;
    left: 16px;
  }
}

/* Portfolio color and typography synchronization */
.navbar-brand,
.page-intro h1,
.library-heading h2,
.learning-card-body strong {
  font-family: "Montserrat", sans-serif;
}

.navbar-brand,
.page-intro h1 {
  font-weight: 800;
}

.library-heading h2,
.learning-card-body strong {
  font-weight: 700;
}

.navbar-nav .nav-link,
button,
.learning-card-topic,
.learning-card-action {
  font-family: "Poppins", sans-serif;
  font-weight: 600;
}

.breadcrumb-nav,
.section-eyebrow,
.learning-card-number,
.learning-card-state {
  font-family: "Inter", "Poppins", sans-serif;
}

.brand-mark {
  background: #000000;
  color: #ffffff;
}

html.dark-mode .brand-mark {
  background: #ffffff;
  color: #000000;
}

.brand-mark,
html.dark-mode .brand-mark {
  overflow: hidden;
  background: transparent;
}

.brand-mark img {
  width: 100%;
  height: 100%;
  display: block;
  object-fit: contain;
}

.btn-theme:focus-visible,
.nav-link:focus-visible,
.navbar-brand:focus-visible,
.navbar-toggler:focus-visible,
.learning-card:focus-visible,
#back-to-top:focus-visible {
  outline-color: var(--ink);
  box-shadow: 0 0 0 3px rgba(0, 0, 0, .08);
}

html.dark-mode .btn-theme:focus-visible,
html.dark-mode .nav-link:focus-visible,
html.dark-mode .navbar-brand:focus-visible,
html.dark-mode .navbar-toggler:focus-visible,
html.dark-mode .learning-card:focus-visible,
html.dark-mode #back-to-top:focus-visible {
  box-shadow: 0 0 0 3px rgba(255, 255, 255, .10);
}

.learning-card-topic i,
.learning-card-state.is-ready {
  color: #ffffff;
}

@media (hover: none) {
  .learning-card-body {
    transform: translateY(0);
  }

  .learning-card-action {
    opacity: 1;
    transform: translateY(0);
  }
}

@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }

  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
  }
}