:root {
  color-scheme: dark;
  background: #0b3450;
}

* {
  box-sizing: border-box;
}

html,
body {
  min-height: 100%;
  margin: 0;
}

body {
  color: #f9fbff;
  background:
    radial-gradient(circle at 50% 0%, rgba(28, 118, 161, 0.35), transparent 44%),
    linear-gradient(180deg, #082b43, #071c2b 72%, #04131e);
  font-family: "Yu Gothic", "Hiragino Kaku Gothic ProN", system-ui, sans-serif;
}

.page-header {
  position: sticky;
  z-index: 2;
  top: 0;
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  min-height: 72px;
  padding: 10px clamp(14px, 4vw, 56px);
  border-bottom: 1px solid rgba(255, 255, 255, 0.16);
  background: rgba(4, 24, 38, 0.86);
  box-shadow: 0 12px 28px rgba(0, 0, 0, 0.22);
  backdrop-filter: blur(14px);
}

.page-header p {
  grid-column: 2;
  margin: 0;
  font-size: clamp(18px, 2vw, 27px);
  font-weight: 800;
  letter-spacing: 0.08em;
}

.back-button {
  grid-column: 1;
  grid-row: 1;
  justify-self: start;
  display: inline-flex;
  align-items: center;
  gap: 8px;
  min-height: 46px;
  padding: 8px 16px;
  color: #fff7dc;
  font-weight: 800;
  text-decoration: none;
  border: 2px solid #5a2d10;
  border-radius: 7px;
  background: linear-gradient(180deg, #985824, #5a3013);
  box-shadow: 0 5px 0 #351d0e, 0 8px 18px rgba(0, 0, 0, 0.28);
}

.back-button:hover,
.back-button:focus-visible {
  filter: brightness(1.14);
  outline: 3px solid rgba(69, 203, 255, 0.6);
  outline-offset: 3px;
}

.development-page {
  width: min(100%, 1120px);
  margin: 0 auto;
  padding: clamp(18px, 4vw, 52px);
}

.development-sheet {
  display: block;
  width: 100%;
  height: auto;
  border-radius: clamp(6px, 1vw, 14px);
  box-shadow: 0 26px 70px rgba(0, 0, 0, 0.52);
}

.development-text {
  width: min(100%, 860px);
  margin: 18px auto 0;
  color: #e7f6ff;
}

.development-text summary {
  width: fit-content;
  margin: 0 auto;
  padding: 7px 15px;
  color: #dff5ff;
  font-size: 12px;
  font-weight: 800;
  letter-spacing: .09em;
  list-style: none;
  border: 1px solid rgba(185, 233, 255, .55);
  border-radius: 999px;
  background: rgba(8, 57, 87, .8);
  cursor: pointer;
}

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

.development-text summary::after {
  content: "＋";
  margin-left: .65em;
}

.development-text[open] summary::after {
  content: "－";
}

.development-text article {
  margin-top: 12px;
  padding: clamp(22px, 4vw, 42px);
  color: #eaf7ff;
  border: 1px solid rgba(185, 233, 255, .28);
  border-radius: 14px;
  background: rgba(4, 31, 49, .88);
  box-shadow: 0 20px 50px rgba(0, 0, 0, .3);
}

.development-text h2 {
  margin: 0 0 24px;
  font-size: clamp(20px, 3vw, 28px);
  letter-spacing: .08em;
}

.development-text p {
  margin: 0;
  font-size: clamp(14px, 1.7vw, 16px);
  line-height: 2;
  letter-spacing: .035em;
}

.development-text p + p {
  margin-top: 1.25em;
}

.visually-hidden {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

@media (max-width: 560px) {
  .page-header {
    min-height: 64px;
  }

  .page-header p {
    justify-self: end;
    grid-column: 3;
    font-size: 16px;
  }

  .back-button {
    padding-inline: 13px;
    font-size: 14px;
  }

  .development-page {
    padding: 14px 8px 28px;
  }

  .development-sheet {
    border-radius: 5px;
  }

  .development-text {
    margin-top: 12px;
  }

  .development-text article {
    padding: 22px 18px;
    border-radius: 10px;
  }

  .development-text p {
    font-size: 14px;
    line-height: 1.9;
  }
}