:root {
  --bg: #0f1419;
  --bg-alt: #151b23;
  --card: #1a2028;
  --border: #2a3441;
  --accent: #29B6F6;
  --text: #c9d1d9;
  --text-muted: #8b949e;
  --white: #f0f3f6;
}

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

html {
  font-size: 16px;
}

body {
  font-family: 'IBM Plex Sans JP', 'IBM Plex Sans', -apple-system, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  padding: 0;
}

/* Mobile-first container */
.container {
  max-width: 800px;
  margin: 0 auto;
  padding: 1.25rem 1rem;
}

/* Header - mobile first */
header {
  position: sticky;
  top: 0;
  background: rgba(15, 20, 25, 0.95);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
  padding: 0.75rem 1rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
  z-index: 100;
}

.logo {
  display: flex;
  align-items: center;
  gap: 0.375rem;
  font-size: 1.15rem;
  text-decoration: none;
}

.logo-icon {
  flex-shrink: 0;
}

.logo-bold {
  font-weight: 700;
  color: var(--white);
}

.logo-light {
  font-weight: 300;
  color: var(--text);
}

.lang-toggle {
  display: flex;
  gap: 0.35rem;
}

.lang-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-muted);
  padding: 0.35rem 0.6rem;
  border-radius: 4px;
  cursor: pointer;
  font-size: 0.75rem;
  transition: all 0.2s;
}

.lang-btn:hover {
  border-color: var(--accent);
  color: var(--accent);
}

.lang-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #000;
}

/* Typography - mobile first */
h1 {
  font-size: 1.5rem;
  font-weight: 600;
  color: var(--white);
  margin-bottom: 0.5rem;
}

h2 {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--white);
  margin: 2rem 0 0.75rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--white);
  margin: 0;
}

p {
  margin-bottom: 1rem;
  color: var(--text);
  font-size: 0.9rem;
}

.subtitle {
  color: var(--text-muted);
  font-size: 0.9rem;
  margin-bottom: 1.5rem;
}

/* Cards - mobile first */
.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem;
  margin-bottom: 1.25rem;
}

.card-title {
  display: flex;
  align-items: flex-start;
  gap: 0.6rem;
  margin-bottom: 0.75rem;
}

.card-icon {
  width: 20px;
  height: 20px;
  color: var(--accent);
  flex-shrink: 0;
  margin-top: 2px;
}

.goal {
  display: inline-block;
  background: rgba(41, 182, 246, 0.1);
  border: 1px solid rgba(41, 182, 246, 0.3);
  color: var(--accent);
  padding: 0.25rem 0.6rem;
  border-radius: 4px;
  font-size: 0.8rem;
  margin-bottom: 0.75rem;
}

/* ===================
   Tables (Desktop only)
   =================== */
.desktop-table {
  display: none;
}

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.8rem;
}

th, td {
  text-align: left;
  padding: 0.6rem 0.5rem;
  border-bottom: 1px solid var(--border);
}

th {
  color: var(--text-muted);
  font-weight: 500;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.5px;
}

td {
  color: var(--text);
}

td strong {
  color: var(--white);
  font-weight: 500;
}

tr:last-child td {
  border-bottom: none;
}

/* ===================
   Mobile Accordion
   =================== */
.mobile-accordion {
  display: block;
  margin: 0.75rem 0;
  border: 1px solid var(--border);
  border-radius: 6px;
  overflow: hidden;
}

.accordion-item {
  border-bottom: 1px solid var(--border);
}

.accordion-item:last-child {
  border-bottom: none;
}

.accordion-header {
  width: 100%;
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 0.75rem 1rem;
  background: var(--bg-alt);
  border: none;
  color: var(--white);
  font-size: 0.85rem;
  font-weight: 500;
  font-family: inherit;
  cursor: pointer;
  text-align: left;
  transition: background 0.2s;
}

.accordion-header:hover {
  background: var(--border);
}

.accordion-title {
  flex: 1;
}

.accordion-chevron {
  width: 18px;
  height: 18px;
  color: var(--text-muted);
  flex-shrink: 0;
  margin-left: 0.5rem;
  transition: transform 0.2s ease;
}

.accordion-header[aria-expanded="true"] .accordion-chevron {
  transform: rotate(180deg);
}

.accordion-content {
  display: none;
  padding: 0.75rem 1rem;
  background: var(--card);
  color: var(--text);
  font-size: 0.85rem;
  line-height: 1.6;
}

.accordion-item.open .accordion-content {
  display: block;
}

/* Highlight box */
.highlight {
  background: rgba(41, 182, 246, 0.08);
  border-left: 3px solid var(--accent);
  padding: 0.75rem 1rem;
  margin: 0.75rem 0;
  border-radius: 0 6px 6px 0;
}

.highlight p {
  margin: 0;
  color: var(--text);
  font-size: 0.85rem;
}

.highlight strong {
  color: var(--accent);
}

/* WP Tag */
.wp-tag {
  color: var(--text-muted);
  font-size: 0.8rem;
  margin-top: 0.75rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--border);
}

/* Why section */
.why-box {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 8px;
  padding: 1.25rem;
}

.why-box p {
  margin-bottom: 0.75rem;
  font-size: 0.9rem;
}

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

.why-box strong {
  color: var(--accent);
}

/* Footer */
footer {
  margin-top: 2rem;
  padding: 1.25rem 1rem;
  border-top: 1px solid var(--border);
  text-align: center;
  color: var(--text-muted);
  font-size: 0.8rem;
}

footer a {
  color: var(--accent);
  text-decoration: none;
}

/* ===================
   Language Switching
   =================== */
.container span[data-lang="en"],
footer span[data-lang="en"],
.mobile-accordion span[data-lang="en"] {
  display: none;
}

.container span[data-lang="ja"],
footer span[data-lang="ja"],
.mobile-accordion span[data-lang="ja"] {
  display: inline;
}

html[lang="en"] .container span[data-lang="en"],
html[lang="en"] footer span[data-lang="en"],
html[lang="en"] .mobile-accordion span[data-lang="en"] {
  display: inline;
}

html[lang="en"] .container span[data-lang="ja"],
html[lang="en"] footer span[data-lang="ja"],
html[lang="en"] .mobile-accordion span[data-lang="ja"] {
  display: none;
}

/* ===================
   Tablet and up (640px)
   =================== */
@media (min-width: 640px) {
  .container {
    padding: 2rem 1.5rem;
  }

  header {
    padding: 1rem 1.5rem;
  }

  .logo {
    font-size: 1.25rem;
  }

  .lang-btn {
    padding: 0.4rem 0.8rem;
    font-size: 0.8rem;
  }

  h1 {
    font-size: 1.75rem;
  }

  h2 {
    font-size: 1.25rem;
    margin: 2.5rem 0 1rem;
  }

  h3 {
    font-size: 1.1rem;
  }

  p, .why-box p {
    font-size: 0.95rem;
  }

  .card {
    padding: 1.5rem;
  }

  .card-icon {
    width: 24px;
    height: 24px;
  }

  /* Switch from accordion to table */
  .mobile-accordion {
    display: none;
  }

  .desktop-table {
    display: table;
  }

  table {
    font-size: 0.85rem;
  }

  th, td {
    padding: 0.75rem;
  }

  td strong {
    white-space: nowrap;
  }
}

/* ===================
   Desktop (768px)
   =================== */
@media (min-width: 768px) {
  .container {
    padding: 2.5rem 2rem;
  }

  h1 {
    font-size: 2rem;
  }

  h2 {
    font-size: 1.35rem;
  }

  p {
    font-size: 1rem;
  }

  .card {
    padding: 1.75rem;
  }

  table {
    font-size: 0.9rem;
  }
}