/* ==========================================================================
   Huanjing Studio — Design System
   HTML5 + CSS3, no frameworks. Mobile first. GitHub Pages friendly.
   ========================================================================== */

/* --------------------------------------------------------------------------
   1. Design Tokens
   -------------------------------------------------------------------------- */
:root {
  /* Color — calm, minimal, trustworthy */
  --color-bg: #ffffff;
  --color-surface: #f6f7f9;
  --color-surface-2: #eef0f4;
  --color-border: #e5e7eb;
  --color-text: #1a1a1f;
  --color-text-muted: #5b6472;
  --color-primary: #4f46e5;
  --color-primary-hover: #4338ca;
  --color-primary-soft: #eef0fe;
  --color-on-primary: #ffffff;
  --color-focus: #6366f1;

  /* Typography */
  --font-sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, "PingFang SC", "Hiragino Sans GB",
    "Microsoft YaHei", "Noto Sans Thai", sans-serif;
  --fs-body: 1rem;
  --lh-body: 1.65;
  --fw-normal: 400;
  --fw-medium: 500;
  --fw-semibold: 600;
  --fw-bold: 700;

  /* Spacing scale */
  --space-1: 0.25rem;
  --space-2: 0.5rem;
  --space-3: 0.75rem;
  --space-4: 1rem;
  --space-5: 1.5rem;
  --space-6: 2rem;
  --space-7: 3rem;
  --space-8: 4rem;
  --space-9: 6rem;

  /* Radius */
  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 20px;
  --radius-pill: 999px;

  /* Shadow — soft, light */
  --shadow-sm: 0 1px 2px rgba(17, 20, 30, 0.06);
  --shadow-md: 0 4px 16px rgba(17, 20, 30, 0.07);
  --shadow-lg: 0 12px 32px rgba(17, 20, 30, 0.09);

  /* Layout */
  --container-max: 1080px;
  --content-max: 720px;
  --header-height: 64px;

  --transition: 160ms ease;
}

/* --------------------------------------------------------------------------
   2. Reset & Base
   -------------------------------------------------------------------------- */
*,
*::before,
*::after {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
  scroll-behavior: smooth;
  scroll-padding-top: calc(var(--header-height) + var(--space-4));
}

body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: var(--fs-body);
  line-height: var(--lh-body);
  color: var(--color-text);
  background-color: var(--color-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

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

a {
  color: var(--color-primary);
  text-decoration: none;
  transition: color var(--transition);
}

a:hover {
  color: var(--color-primary-hover);
  text-decoration: underline;
}

h1,
h2,
h3,
h4 {
  line-height: 1.25;
  font-weight: var(--fw-bold);
  color: var(--color-text);
  margin: 0 0 var(--space-4);
  letter-spacing: -0.01em;
}

h1 {
  font-size: clamp(2rem, 5vw, 3.25rem);
  letter-spacing: -0.02em;
}

h2 {
  font-size: clamp(1.5rem, 3.2vw, 2.125rem);
}

h3 {
  font-size: 1.25rem;
}

p {
  margin: 0 0 var(--space-4);
}

ul,
ol {
  margin: 0 0 var(--space-4);
  padding-left: 1.35rem;
}

li {
  margin-bottom: var(--space-2);
}

hr {
  border: none;
  border-top: 1px solid var(--color-border);
  margin: var(--space-7) 0;
}

/* Visible focus for keyboard users (accessibility) */
:focus-visible {
  outline: 3px solid var(--color-focus);
  outline-offset: 2px;
  border-radius: var(--radius-sm);
}

/* Screen-reader only helper */
.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

/* Skip link */
.skip-link {
  position: absolute;
  left: var(--space-4);
  top: -100px;
  z-index: 200;
  background: var(--color-primary);
  color: var(--color-on-primary);
  padding: var(--space-2) var(--space-4);
  border-radius: var(--radius-sm);
  transition: top var(--transition);
}

.skip-link:focus {
  top: var(--space-3);
  color: var(--color-on-primary);
  text-decoration: none;
}

/* --------------------------------------------------------------------------
   3. Layout helpers
   -------------------------------------------------------------------------- */
.container {
  width: 100%;
  max-width: var(--container-max);
  margin-inline: auto;
  padding-inline: var(--space-5);
}

.section {
  padding-block: var(--space-8);
}

.section--tight {
  padding-block: var(--space-7);
}

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

.text-center {
  text-align: center;
}

.lead {
  font-size: 1.15rem;
  color: var(--color-text-muted);
  max-width: 42ch;
}

.eyebrow {
  display: inline-block;
  font-size: 0.8rem;
  font-weight: var(--fw-semibold);
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--color-primary);
  margin-bottom: var(--space-3);
}

/* --------------------------------------------------------------------------
   4. Buttons
   -------------------------------------------------------------------------- */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  font-family: inherit;
  font-size: 1rem;
  font-weight: var(--fw-semibold);
  line-height: 1;
  padding: 0.8rem 1.4rem;
  border-radius: var(--radius-md);
  border: 1px solid transparent;
  cursor: pointer;
  transition: background-color var(--transition), border-color var(--transition),
    color var(--transition), transform var(--transition), box-shadow var(--transition);
  text-decoration: none;
  white-space: nowrap;
}

.btn:hover {
  text-decoration: none;
}

.btn:active {
  transform: translateY(1px);
}

.btn--primary {
  background-color: var(--color-primary);
  color: var(--color-on-primary);
  box-shadow: var(--shadow-sm);
}

.btn--primary:hover {
  background-color: var(--color-primary-hover);
  color: var(--color-on-primary);
  box-shadow: var(--shadow-md);
}

.btn--secondary {
  background-color: var(--color-bg);
  color: var(--color-text);
  border-color: var(--color-border);
}

.btn--secondary:hover {
  background-color: var(--color-surface);
  color: var(--color-text);
  border-color: var(--color-text-muted);
}

.btn--ghost {
  background-color: transparent;
  color: var(--color-primary);
}

.btn--ghost:hover {
  background-color: var(--color-primary-soft);
  color: var(--color-primary-hover);
}

/* Store badge buttons (Coming Soon) */
.store-badges {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  margin-top: var(--space-5);
}

.store-badge {
  display: inline-flex;
  flex-direction: column;
  align-items: flex-start;
  padding: 0.6rem 1.1rem;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-surface);
  color: var(--color-text-muted);
  min-width: 190px;
  cursor: default;
}

.store-badge .store-badge__label {
  font-size: 0.72rem;
  letter-spacing: 0.02em;
}

.store-badge .store-badge__name {
  font-size: 1.05rem;
  font-weight: var(--fw-semibold);
  color: var(--color-text);
}

.store-badge .store-badge__status {
  margin-top: var(--space-1);
  font-size: 0.72rem;
  font-weight: var(--fw-semibold);
  letter-spacing: 0.04em;
  text-transform: uppercase;
  color: var(--color-primary);
}

/* --------------------------------------------------------------------------
   5. Header / Navigation
   -------------------------------------------------------------------------- */
.site-header {
  position: sticky;
  top: 0;
  z-index: 100;
  background-color: rgba(255, 255, 255, 0.9);
  backdrop-filter: saturate(180%) blur(10px);
  -webkit-backdrop-filter: saturate(180%) blur(10px);
  border-bottom: 1px solid var(--color-border);
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  min-height: var(--header-height);
}

.brand {
  font-size: 1.15rem;
  font-weight: var(--fw-bold);
  color: var(--color-text);
  letter-spacing: -0.01em;
  display: inline-flex;
  align-items: center;
  gap: var(--space-2);
}

.brand:hover {
  color: var(--color-text);
  text-decoration: none;
}

.brand__mark {
  width: 26px;
  height: 26px;
  flex: none;
}

.nav-toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 42px;
  height: 42px;
  border: 1px solid var(--color-border);
  border-radius: var(--radius-sm);
  background: var(--color-bg);
  cursor: pointer;
  color: var(--color-text);
}

.nav-toggle:hover {
  background: var(--color-surface);
}

.nav-toggle__bars,
.nav-toggle__bars::before,
.nav-toggle__bars::after {
  content: "";
  display: block;
  width: 20px;
  height: 2px;
  background: currentColor;
  border-radius: 2px;
  transition: transform var(--transition), opacity var(--transition);
}

.nav-toggle__bars {
  position: relative;
}

.nav-toggle__bars::before {
  position: absolute;
  top: -6px;
}

.nav-toggle__bars::after {
  position: absolute;
  top: 6px;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars {
  background: transparent;
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars::before {
  top: 0;
  transform: rotate(45deg);
}

.nav-toggle[aria-expanded="true"] .nav-toggle__bars::after {
  top: 0;
  transform: rotate(-45deg);
}

.site-nav ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: flex;
  align-items: center;
  gap: var(--space-2);
}

.site-nav a {
  display: inline-block;
  padding: var(--space-2) var(--space-3);
  border-radius: var(--radius-sm);
  color: var(--color-text-muted);
  font-weight: var(--fw-medium);
}

.site-nav a:hover {
  color: var(--color-text);
  background: var(--color-surface);
  text-decoration: none;
}

.site-nav a[aria-current="page"] {
  color: var(--color-primary);
  font-weight: var(--fw-semibold);
}

/* Mobile behaviour */
@media (max-width: 767px) {
  .site-nav {
    position: absolute;
    left: 0;
    right: 0;
    top: 100%;
    background: var(--color-bg);
    border-bottom: 1px solid var(--color-border);
    box-shadow: var(--shadow-md);
    display: none;
  }

  .site-nav.is-open {
    display: block;
  }

  .site-nav ul {
    flex-direction: column;
    align-items: stretch;
    gap: 0;
    padding: var(--space-3) var(--space-5) var(--space-5);
  }

  .site-nav a {
    padding: var(--space-3) var(--space-2);
    border-radius: var(--radius-sm);
    font-size: 1.05rem;
  }
}

@media (min-width: 768px) {
  .nav-toggle {
    display: none;
  }

  .site-nav {
    display: block !important;
  }
}

/* --------------------------------------------------------------------------
   6. Hero
   -------------------------------------------------------------------------- */
.hero {
  padding-block: clamp(var(--space-8), 12vw, 7rem);
  text-align: center;
}

.hero__inner {
  max-width: 780px;
  margin-inline: auto;
}

.hero h1 {
  margin-bottom: var(--space-4);
}

.hero .lead {
  margin-inline: auto;
  max-width: 52ch;
  font-size: 1.2rem;
}

.hero__actions {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-3);
  justify-content: center;
  margin-top: var(--space-6);
}

/* --------------------------------------------------------------------------
   7. Cards & grids
   -------------------------------------------------------------------------- */
.grid {
  display: grid;
  gap: var(--space-5);
}

@media (min-width: 640px) {
  .grid--2 {
    grid-template-columns: repeat(2, 1fr);
  }
}

@media (min-width: 900px) {
  .grid--3 {
    grid-template-columns: repeat(3, 1fr);
  }
}

.card {
  background: var(--color-bg);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-lg);
  padding: var(--space-6);
  box-shadow: var(--shadow-sm);
  transition: box-shadow var(--transition), transform var(--transition),
    border-color var(--transition);
}

.card h3 {
  margin-bottom: var(--space-2);
}

/* Product card */
.product-card {
  display: flex;
  flex-direction: column;
}

.product-card:hover {
  box-shadow: var(--shadow-lg);
  transform: translateY(-3px);
  border-color: var(--color-surface-2);
}

.product-card__head {
  display: flex;
  align-items: center;
  gap: var(--space-4);
  margin-bottom: var(--space-4);
}

.product-card__icon {
  width: 64px;
  height: 64px;
  flex: none;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.product-card__title {
  margin: 0;
  font-size: 1.3rem;
}

.product-card__subtitle {
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

.product-card__tagline {
  color: var(--color-primary);
  font-weight: var(--fw-semibold);
  margin-bottom: var(--space-3);
}

.product-card__body {
  color: var(--color-text-muted);
  flex: 1;
}

.product-card__actions {
  margin-top: var(--space-5);
}

/* Feature list */
.feature-list {
  list-style: none;
  padding: 0;
  margin: 0;
  display: grid;
  gap: var(--space-4);
}

@media (min-width: 640px) {
  .feature-list {
    grid-template-columns: repeat(2, 1fr);
  }
}

.feature-list li {
  margin: 0;
  padding-left: 1.9rem;
  position: relative;
  color: var(--color-text);
}

.feature-list li::before {
  content: "";
  position: absolute;
  left: 0;
  top: 0.45em;
  width: 12px;
  height: 12px;
  border-radius: 50%;
  background: var(--color-primary-soft);
  border: 3px solid var(--color-primary);
}

.feature-list li strong {
  display: block;
  font-weight: var(--fw-semibold);
}

.feature-list li span {
  color: var(--color-text-muted);
  font-size: 0.95rem;
}

/* --------------------------------------------------------------------------
   8. Product detail hero
   -------------------------------------------------------------------------- */
.product-hero {
  display: grid;
  gap: var(--space-6);
  align-items: center;
  padding-block: var(--space-8);
}

@media (min-width: 768px) {
  .product-hero {
    grid-template-columns: 140px 1fr;
    gap: var(--space-7);
  }
}

.product-hero__icon {
  width: 120px;
  height: 120px;
  border-radius: 26px;
  box-shadow: var(--shadow-md);
}

.product-hero__names {
  display: flex;
  flex-wrap: wrap;
  align-items: baseline;
  gap: var(--space-3);
  margin-bottom: var(--space-3);
}

.product-hero__cn {
  color: var(--color-text-muted);
  font-size: 1.4rem;
  font-weight: var(--fw-medium);
}

/* --------------------------------------------------------------------------
   9. Callout / info box
   -------------------------------------------------------------------------- */
.callout {
  background: var(--color-primary-soft);
  border: 1px solid #dcdcfb;
  border-radius: var(--radius-md);
  padding: var(--space-5);
}

.callout--muted {
  background: var(--color-surface);
  border-color: var(--color-border);
}

.callout p:last-child {
  margin-bottom: 0;
}

/* --------------------------------------------------------------------------
   10. Footer
   -------------------------------------------------------------------------- */
.site-footer {
  background: var(--color-surface);
  border-top: 1px solid var(--color-border);
  padding-block: var(--space-8) var(--space-6);
  margin-top: var(--space-9);
}

.site-footer__grid {
  display: grid;
  gap: var(--space-6);
  grid-template-columns: 1fr;
}

@media (min-width: 640px) {
  .site-footer__grid {
    grid-template-columns: 1.4fr 1fr 1fr;
  }
}

.site-footer h4 {
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-text-muted);
  margin-bottom: var(--space-3);
}

.site-footer ul {
  list-style: none;
  margin: 0;
  padding: 0;
}

.site-footer li {
  margin-bottom: var(--space-2);
}

.site-footer a {
  color: var(--color-text);
  font-weight: var(--fw-medium);
}

.site-footer a:hover {
  color: var(--color-primary);
}

.site-footer__brand p {
  color: var(--color-text-muted);
  max-width: 32ch;
  margin-top: var(--space-2);
}

.site-footer__bottom {
  margin-top: var(--space-7);
  padding-top: var(--space-5);
  border-top: 1px solid var(--color-border);
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2) var(--space-4);
  align-items: center;
  justify-content: space-between;
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

/* --------------------------------------------------------------------------
   11. Document pages (Privacy / Terms / Support / About)
   -------------------------------------------------------------------------- */
.doc {
  max-width: var(--content-max);
  margin-inline: auto;
  padding-block: var(--space-7) var(--space-8);
}

.doc__header {
  margin-bottom: var(--space-6);
  padding-bottom: var(--space-5);
  border-bottom: 1px solid var(--color-border);
}

.doc__app-name {
  font-weight: var(--fw-semibold);
  color: var(--color-primary);
  margin-bottom: var(--space-2);
}

.doc__title {
  margin-bottom: var(--space-2);
}

.doc__updated {
  color: var(--color-text-muted);
  font-size: 0.95rem;
  margin: 0;
}

.doc h2 {
  font-size: 1.3rem;
  margin-top: var(--space-7);
  scroll-margin-top: calc(var(--header-height) + var(--space-4));
}

.doc h2:first-of-type {
  margin-top: var(--space-5);
}

.doc .section {
  padding-block: 0;
  margin-bottom: var(--space-4);
}

/* Table of contents */
.toc {
  background: var(--color-surface);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  padding: var(--space-5);
  margin-bottom: var(--space-6);
}

.toc strong {
  display: block;
  margin-bottom: var(--space-3);
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--color-text-muted);
}

.toc a {
  display: block;
  padding: var(--space-1) 0;
  color: var(--color-text);
  font-size: 0.95rem;
}

.toc a:hover {
  color: var(--color-primary);
}

/* Language switcher */
.language-switcher {
  display: flex;
  flex-wrap: wrap;
  gap: var(--space-2);
  margin-bottom: var(--space-6);
}

.language-switcher a {
  padding: var(--space-1) var(--space-3);
  border: 1px solid var(--color-border);
  border-radius: var(--radius-pill);
  font-size: 0.9rem;
  color: var(--color-text-muted);
  background: var(--color-bg);
}

.language-switcher a:hover {
  color: var(--color-text);
  border-color: var(--color-text-muted);
  text-decoration: none;
}

.language-switcher a.active {
  background: var(--color-primary);
  border-color: var(--color-primary);
  color: var(--color-on-primary);
}

/* FAQ (details/summary) */
.faq {
  display: grid;
  gap: var(--space-3);
  margin-bottom: var(--space-5);
}

.faq details {
  border: 1px solid var(--color-border);
  border-radius: var(--radius-md);
  background: var(--color-bg);
  overflow: hidden;
}

.faq summary {
  cursor: pointer;
  padding: var(--space-4);
  font-weight: var(--fw-semibold);
  list-style: none;
  position: relative;
  padding-right: var(--space-7);
}

.faq summary::-webkit-details-marker {
  display: none;
}

.faq summary::after {
  content: "+";
  position: absolute;
  right: var(--space-4);
  top: 50%;
  transform: translateY(-50%);
  font-size: 1.3rem;
  color: var(--color-text-muted);
  line-height: 1;
}

.faq details[open] summary::after {
  content: "\2212"; /* minus */
}

.faq summary:hover {
  background: var(--color-surface);
}

.faq details[open] summary {
  border-bottom: 1px solid var(--color-border);
}

.faq p {
  padding: var(--space-4);
  margin: 0;
  color: var(--color-text-muted);
}

.contact-email {
  font-weight: var(--fw-semibold);
}

.doc__footer {
  margin-top: var(--space-7);
  padding-top: var(--space-5);
  border-top: 1px solid var(--color-border);
  color: var(--color-text-muted);
  font-size: 0.9rem;
}

/* Pending / TODO badge for not-yet-configured contact info */
.pending {
  display: inline-block;
  font-size: 0.75rem;
  font-weight: var(--fw-semibold);
  letter-spacing: 0.03em;
  text-transform: uppercase;
  color: var(--color-text-muted);
  background: var(--color-surface-2);
  border-radius: var(--radius-pill);
  padding: 0.15rem 0.6rem;
  margin-left: var(--space-2);
  vertical-align: middle;
}

/* --------------------------------------------------------------------------
   12. 404
   -------------------------------------------------------------------------- */
.error-page {
  min-height: 60vh;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding-block: var(--space-8);
}

.error-page .error-code {
  font-size: clamp(3.5rem, 12vw, 6rem);
  font-weight: var(--fw-bold);
  color: var(--color-primary);
  line-height: 1;
  margin-bottom: var(--space-4);
}

/* --------------------------------------------------------------------------
   13. Reduced motion
   -------------------------------------------------------------------------- */
@media (prefers-reduced-motion: reduce) {
  html {
    scroll-behavior: auto;
  }
  *,
  *::before,
  *::after {
    transition-duration: 0.01ms !important;
    animation-duration: 0.01ms !important;
  }
}