body {
  width:100%;
  max-width: 900px;
  margin: 0 auto;
  font-family: "Segoe UI", "Hiragino Kaku Gothic ProN", sans-serif;
  background-color: #f0f8ff;
  color: #333;
  padding: 0;
}

p{
  font-size: 1em;
}

header {
  background-color: #a0d8ef;
  padding: 2em;
  text-align: center;
  border-bottom: 4px solid #7ec0ee;
}

header h1 {
  margin: 0;
  font-size: 2em;
}

header p {
  margin-top: 0.5em;
  font-size: 1.2em;
  color: #444;
}

section {
  min-height: 95vh;
  padding: 2em;
  border-bottom: 1px dashed #ccc;
}

section h2 {
  color: #2b7bb9;
  margin-bottom: 0.5em;
}

section h3 {
  color: #3a9bdc;
  margin: 1.5em 0.5em -0.8em 1em;
}

ul, ol {
  margin-left: 1.5em;
}

img {
  display: block;
  margin: 1em auto;
  max-width: 100%;
  height: auto;
}

footer {
  background-color: #e0f7fa;
  text-align: center;
  padding: 1em;
  font-size: 0.9em;
  color: #666;
}

/* スムーズスクロール */
html {
  scroll-behavior: smooth;
}

/* トップに戻るボタン */
.to-top{
  position: fixed;
  top: 16px;
  right: 16px;
  z-index: 1000;
  display: inline-block;
  color: #999;
  padding: 8px 12px;
  border-radius: 4px;
  text-decoration: none;
  font-weight: 600;
  box-shadow: 0 2px 6px rgba(0,0,0,0.2);
  transition: background-color .15s, transform .12s;
  font-size: 20px;
}

/* ホバー/フォーカス時 */
.to-top:hover,
.to-top:focus{
  transform: translateY(-2px);
  outline: none;
}
.flex15 {
  display: flex;
  justify-content: space-between;
  font-size:20px;
}

.flex15 div {
  width:50%;
  flex: 1;
}

/* 小さい画面で少しサイズ調整 */
@media (max-width:480px){
  .to-top{
    top: 12px;
    right: 12px;
    padding: 1px;
  }
}