:root {
  --navy: #0c1c45;
  --text: #3a4256;
  --bg: #f7f8fa;
  --line: #dde2ec;
}

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

body {
  font-family: "Poppins", system-ui, -apple-system, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

header {
  padding: 20px max(16px, 4.9vw);
}
header img { display: block; width: 132px; height: auto; }

main {
  max-width: 760px;
  margin: 0 auto;
  padding: 2rem 16px 4rem;
}

h1 {
  font-size: clamp(2rem, 4vw, 2.8rem);
  font-weight: 700;
  line-height: 1.15;
  color: var(--navy);
  margin-bottom: 2rem;
}

h2 {
  font-size: 1.15rem;
  font-weight: 700;
  color: var(--navy);
  margin: 2.2rem 0 0.6rem;
}

h3 {
  font-size: 1rem;
  font-weight: 500;
  color: var(--navy);
  margin: 1.4rem 0 0.4rem;
}

p, ul { margin-bottom: 0.9rem; }
ul { padding-left: 1.3rem; }
a { color: var(--navy); }

.todo {
  background: #ffe1e1;
  color: #b3141c;
  font-weight: 700;
  padding: 0 0.3em;
  border-radius: 3px;
}

.optional {
  border-left: 3px solid #f0b400;
  background: #fff8e1;
  padding: 0.8rem 1rem;
  margin: 1rem 0;
  border-radius: 0 4px 4px 0;
}
.optional > small {
  display: block;
  font-weight: 700;
  color: #8a6400;
  margin-bottom: 0.3rem;
}

.back {
  display: inline-block;
  margin-top: 2.5rem;
  font-weight: 500;
  text-decoration: none;
}
.back:hover { text-decoration: underline; }

footer {
  border-top: 1px solid var(--line);
  padding: 1.2rem 16px;
  display: flex;
  justify-content: center;
  gap: 1.6rem;
  font-size: 0.85rem;
}
footer a { color: var(--text); text-decoration: none; }
footer a:hover { color: var(--navy); text-decoration: underline; }