*, *::before, *::after { box-sizing: border-box; }
html { scroll-padding-top: 100px; }
body { margin: 0; padding-top: 100px; padding-bottom: 60px; }

.background {
  position: fixed; top: 0; left: 0;
  width: 100%; height: 100%;
  background: url('../background.jpg') no-repeat center / cover;
  z-index: -1;
}
header {
  width: 100%; background: #ffffff; color: #282928;
  padding: 15px 50px; position: fixed; top: 0; left: 0; z-index: 10;
}
.header-top {
  display: flex; align-items: center;
  justify-content: space-between; width: 100%;
}
header h1 { margin: 0; }
header h1 img { display: block; height: 40px; width: auto; opacity: 0.9; }
.tabs {
  display: flex; flex: 1; gap: 4px;
  margin-left: 40px;
  border-bottom: 1.5px solid rgba(0,0,0,0.2);
}
.tab-btn {
  flex: 1; text-align: center; background: none; border: none;
  border-bottom: 2.5px solid transparent; margin-bottom: -1.5px;
  padding: 8px 16px; font-size: 14px; color: rgba(0,0,0,0.5);
  cursor: pointer; transition: color 0.2s;
}
.tab-btn.active { color: #282928; border-bottom-color: #282928; font-weight: 500; }
.tab-btn:hover { color: rgba(0,0,0,0.8); }
.tab-panel { display: none; }
.tab-panel.active { display: block; }
h2 {
  display: inline-block; font-size: 20px; font-weight: 500;
  border-radius: 6px; padding: 8px 24px;
  background: #E6F1FB; color: #0C447C; margin: 0 0 16px;
}
.content-box {
  display: block; width: min(90%, 800px); margin: 20px auto; padding: 30px;
  background-color: rgba(123,129,116,0.85); border-radius: 10px;
  font-size: 18px; color: white; box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}
footer {
  width: 100%; background: #ffffff; color: #000000;
  text-align: center; padding: 15px 0;
  position: fixed; bottom: 0; left: 0; z-index: 10;
}

/* ===== スマホ ===== */
@media (max-width: 768px) {
  .header-top {
    flex-direction: column;
    align-items: center; /* ★flex-startからcenterに変更 */
  }
  .tabs {
    margin-left: 0;
    margin-top: 8px;
    width: 100%;
  }
  .content-box {
    width: 95%;
    padding: 20px;
    font-size: 16px;
  }
  body {
    padding-top: 160px;
  }
}