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

html {
  scroll-behavior: smooth;
  -webkit-text-size-adjust: 100%;
}

body {
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
  background-color: var(--clr-bg, #FFFFFF);
  color: var(--clr-text, #1F2937);
  line-height: 1.6;
  min-height: 100vh;
  padding-top: 4rem;
}

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

/* 2. ROOT VARIABLES */
:root {
  --clr-accent: #10B981;
  --clr-bg: #F9FAFB;
  --clr-text: #1F2937;
  --clr-heading: #111827;
  --radius: 0.5rem;
  --shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
  --max-width: 1200px;
  --spacing: 1rem;
}

/* Theme variations */
.theme-blue {
  --clr-accent: #3B82F6;
}

.theme-pink {
  --clr-accent: #EC4899;
}

.theme-orange {
  --clr-accent: #F97316;
}

/* 3. CONTAINER */
.container {
  width: 90%;
  max-width: var(--max-width);
  margin-inline: auto;
  padding-inline: var(--spacing);
}

/* 4. TYPOGRAPHY */
h1,
h2,
h3,
h4,
h5,
h6 {
  color: var(--clr-heading);
  font-weight: 700;
  line-height: 1.2;
  margin-block: 1.5rem 1rem;
}

h1 {
  font-size: 2rem;
}

h2 {
  font-size: 1.75rem;
}

h3 {
  font-size: 1.5rem;
}

p,
ul,
ol,
blockquote,
table {
  margin-block: 1rem;
}

ul,
ol {
  padding-inline-start: 1.25rem;
}

a {
  color: var(--clr-accent);
  text-decoration: none;
  transition: opacity 0.2s ease-in-out;
}

a:hover,
a:focus {
  opacity: 0.8;
}

/* 5. BUTTONS */
.btn,
button {
  display: inline-block;
  background-color: var(--clr-accent);
  color: #FFFFFF;
  font-weight: 600;
  padding: 0.75rem 1.5rem;
  border: none;
  border-radius: var(--radius);
  cursor: pointer;
  box-shadow: var(--shadow);
  text-align: center;
  transition: transform 0.1s ease, opacity 0.2s ease;
}

.btn:hover,
button:hover {
  opacity: 0.9;
  transform: translateY(-2px);
}

/* 6. CARD COMPONENT */
.card {
  background-color: #FFFFFF;
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 1.5rem;
  margin-block: 1.5rem;
}

/* 7. HEADER & FOOTER */
header {
  position: sticky;
  top: 0;
  width: 100%;
  background-color: #FFFFFF;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.05);
  z-index: 1000;
}

footer {
  background-color: #111827;
  color: #FFFFFF;
  text-align: center;
  font-size: 0.875rem;
  padding-block: 2rem 1rem;
}

/* 8. LAYOUT UTILITIES */
.text-center {
  text-align: center;
}

.mt-1 {
  margin-top: 0.25rem;
}

.mt-2 {
  margin-top: 0.5rem;
}

.mt-4 {
  margin-top: 1rem;
}

.mb-4 {
  margin-bottom: 1rem;
}

.p-4 {
  padding: 1rem;
}

.grid {
  display: grid;
  gap: 1rem;
}

/* 9. RESPONSIVE BREAKPOINTS */
@media (min-width: 640px) {
  h1 {
    font-size: 2.5rem;
  }

  h2 {
    font-size: 2rem;
  }

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

@media (min-width: 768px) {
  h1 {
    font-size: 3rem;
  }

  .grid-cols-3 {
    grid-template-columns: repeat(3, 1fr);
  }
}

@media (min-width: 1024px) {
  .container {
    padding-inline: 2rem;
  }
}

/* 10. TABLES & BLOCKQUOTE */
table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
  margin-block: 1.5rem;
}

th,
td {
  border: 1px solid #E5E7EB;
  padding: 0.75rem;
  text-align: left;
}

th {
  background-color: #F3F4F6;
}

blockquote {
  border-left: 4px solid var(--clr-accent);
  background-color: #F3F4F6;
  padding: 1rem 1.5rem;
  border-radius: var(--radius);
  margin-block: 1.5rem;
}

/* 11. CODE BLOCKS */
code {
  background-color: #F3F4F6;
  padding: 0.2em 0.4em;
  border-radius: 0.25em;
  font-size: 0.9em;
}

pre {
  background-color: #F3F4F6;
  padding: 1rem;
  border-radius: var(--radius);
  overflow-x: auto;
  margin-block: 1.5rem;
}

/* フェードイン用 */
.fade-in {
  opacity: 0;
  transform: translateY(20px);
  transition: opacity 0.6s ease-out, transform 0.6s ease-out;
}

.appear {
  opacity: 1;
  transform: translateY(0);
}

/* Back to Top ボタン */
#backToTop:hover {
  opacity: 0.8;
}

.markdown-body {
  max-width: 980px;
  margin: 0 auto;
  padding: 24px;
  font-family: 'Segoe UI', Arial, sans-serif;
  font-size: 16px;
  background: #fff;
  color: #24292e;
}

/* スマホ対応 */
@media (max-width: 767px) {
  .markdown-body {
    padding: 8px;
    font-size: 15px;
  }
}

/* 必要ならtableやimgもここにまとめる */



/* ─── 見出しのレスポンシブ再設定 ─── */
h1,
h2,
h3 {
  margin-block: 1.5rem 1rem;
  line-height: 1.2;
  font-weight: 700;
  color: var(--clr-heading);
}

@media (max-width: 639px) {
  h1 {
    font-size: 2.5rem;
  }

  /* ≒40px */
  h2 {
    font-size: 2.25rem;
  }

  /* ≒36px */
  h3 {
    font-size: 2rem;
  }

  /* ≒32px */
}

@media (min-width: 640px) {
  h1 {
    font-size: 3rem;
  }

  /* ≒48px */
  h2 {
    font-size: 2.5rem;
  }

  /* ≒40px */
  h3 {
    font-size: 2.25rem;
  }

  /* ≒36px */
}

@media (min-width: 768px) {
  h1 {
    font-size: 3.5rem;
  }

  /* ≒56px */
  h2 {
    font-size: 3rem;
  }

  /* ≒48px */
  h3 {
    font-size: 2.5rem;
  }

  /* ≒40px */
}

/* 格安シムのカードを3つずつ並べる */
.company-grid {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 1rem;
}

.banner-image {
  max-width: 100%;
  height: auto;
}

.ad-banner-container {
  max-width: 468px;
  /* 箱の横幅は最大でも468pxにする */
  margin: 2rem auto;
  /* 箱をページの中央に配置する */
}