:root {
  --paper: #FAF7F0;
  --ink: #141414;
  --green: #2ECC71;
  --coral: #E74C3C;
  --amber: #F59E0B;
  --gray: #6b7280;
  --card: #FFFFFF;
  --mono: "Menlo", "SF Mono", Consolas, monospace;
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  background: var(--paper);
  color: var(--ink);
  font-family: -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.65;
  font-size: 17px;
}
.wrap { max-width: 860px; margin: 0 auto; padding: 0 22px; }

/* header */
header.site {
  border-bottom: 3px solid var(--ink);
  background: var(--paper);
}
header.site .wrap {
  display: flex; align-items: center; justify-content: space-between;
  padding-top: 18px; padding-bottom: 18px; gap: 16px; flex-wrap: wrap;
}
.logo { font-weight: 900; font-size: 1.35rem; letter-spacing: .02em; text-decoration: none; color: var(--ink); }
.logo span { color: var(--green); }
nav.main a {
  color: var(--ink); text-decoration: none; font-weight: 600; font-size: .95rem;
  margin-left: 18px;
}
nav.main a:hover { color: var(--green); }

/* hero */
.hero { padding: 64px 0 40px; }
.hero h1 {
  font-weight: 900; font-size: clamp(1.9rem, 5vw, 3.1rem); line-height: 1.12;
  letter-spacing: -.01em;
}
.hero h1 em { font-style: normal; color: var(--green); }
.hero p.sub { margin-top: 18px; font-size: 1.15rem; color: #333; max-width: 620px; }
.badge {
  display: inline-block; border: 2px solid var(--coral); color: var(--coral);
  border-radius: 999px; padding: 3px 14px; font-weight: 700; font-size: .8rem;
  letter-spacing: .04em; margin-bottom: 18px;
}

/* buttons */
.btn {
  display: inline-block; background: var(--ink); color: var(--paper);
  padding: 12px 22px; border-radius: 10px; text-decoration: none; font-weight: 700;
  border: none; cursor: pointer; font-size: 1rem;
}
.btn:hover { background: #000; }
.btn.green { background: var(--green); color: #06301a; }
.btn.green:hover { filter: brightness(1.05); }
.btn.ghost { background: transparent; color: var(--ink); border: 2px solid var(--ink); }

/* cards */
.grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(250px, 1fr)); gap: 18px; margin: 26px 0 10px; }
.card {
  background: var(--card); border: 2px solid var(--ink); border-radius: 14px;
  padding: 22px; display: flex; flex-direction: column; gap: 8px;
  box-shadow: 4px 4px 0 rgba(20,20,20,.9);
  transition: transform .08s ease;
}
.card:hover { transform: translate(-1px,-1px); }
.card .tag { font-size: .72rem; font-weight: 800; letter-spacing: .08em; }
.tag.free { color: var(--green); }
.tag.math { color: var(--amber); }
.card h3 { font-size: 1.12rem; font-weight: 800; line-height: 1.3; }
.card p { font-size: .93rem; color: #3b3b3b; flex-grow: 1; }
.card a.cardlink { color: var(--ink); font-weight: 700; text-decoration: none; font-size: .95rem; }
.card a.cardlink:hover { color: var(--green); }
.card a.stretch::after { content: ""; position: absolute; inset: 0; }
.card { position: relative; }

/* sections */
section { padding: 34px 0; }
h2.section {
  font-weight: 900; font-size: 1.5rem; margin-bottom: 6px;
  border-bottom: 4px solid var(--green); display: inline-block; padding-bottom: 4px;
}
h2.section.coral { border-color: var(--coral); }
h2.section.amber { border-color: var(--amber); }

/* article pages */
article.post { padding: 46px 0 20px; }
article.post h1 { font-weight: 900; font-size: clamp(1.6rem, 4.5vw, 2.4rem); line-height: 1.15; margin-bottom: 10px; }
article.post .meta { color: var(--gray); font-size: .9rem; margin-bottom: 26px; }
article.post h2 { font-weight: 800; font-size: 1.3rem; margin: 34px 0 10px; }
article.post p { margin: 14px 0; }
article.post ul, article.post ol { margin: 14px 0 14px 26px; }
article.post li { margin: 7px 0; }
.big-number {
  font-weight: 900; font-size: clamp(2.2rem, 7vw, 3.6rem); line-height: 1;
  margin: 26px 0 4px;
}
.big-number.green { color: var(--green); }
.big-number.coral { color: var(--coral); }
.big-number.amber { color: var(--amber); }
.big-caption { color: var(--gray); font-size: .95rem; margin-bottom: 18px; }

/* prompt blocks */
.promptbox {
  position: relative; background: #1c1e26; color: #e8e8e8;
  border-radius: 12px; border: 2px solid var(--ink);
  padding: 46px 20px 20px; margin: 20px 0; font-family: var(--mono);
  font-size: .88rem; line-height: 1.6; white-space: pre-wrap; overflow-x: auto;
}
.promptbox .copybtn {
  position: absolute; top: 10px; right: 10px;
  background: var(--green); color: #06301a; border: none; border-radius: 8px;
  font-weight: 800; font-size: .78rem; padding: 6px 12px; cursor: pointer;
  font-family: inherit;
}
.promptbox .copybtn:hover { filter: brightness(1.08); }
.promptlabel { font-weight: 800; font-size: .8rem; letter-spacing: .07em; color: var(--amber); margin-top: 26px; }

/* callouts */
.callout {
  border-left: 6px solid var(--amber); background: #fff7e8;
  padding: 14px 18px; border-radius: 0 10px 10px 0; margin: 20px 0; font-size: .95rem;
}
.callout.red { border-color: var(--coral); background: #fdeeec; }
.callout.green { border-color: var(--green); background: #eafaf1; }

/* tables */
table.numbers { border-collapse: collapse; width: 100%; margin: 18px 0; font-size: .95rem; }
table.numbers th, table.numbers td { border: 2px solid var(--ink); padding: 9px 12px; text-align: left; }
table.numbers th { background: var(--ink); color: var(--paper); font-size: .85rem; letter-spacing: .03em; }
table.numbers td.num { font-family: var(--mono); font-size: .9rem; }

/* email box */
.emailbox {
  border: 2px dashed var(--ink); border-radius: 14px; padding: 26px; margin: 30px 0;
  background: var(--card);
}
.emailbox h3 { font-weight: 900; font-size: 1.15rem; }
.emailbox p { font-size: .95rem; color: #3b3b3b; margin: 8px 0 0; }

/* video cta */
.videocta {
  display: flex; align-items: center; gap: 14px; border: 2px solid var(--ink);
  border-radius: 12px; padding: 16px 18px; margin: 26px 0; background: var(--card);
  text-decoration: none; color: var(--ink);
  box-shadow: 4px 4px 0 rgba(20,20,20,.9);
}
.videocta:hover { transform: translate(-1px,-1px); }
.videocta .play {
  width: 46px; height: 46px; border-radius: 50%; background: var(--coral);
  color: #fff; display: flex; align-items: center; justify-content: center;
  font-size: 1.1rem; flex-shrink: 0;
}
.videocta div b { display: block; font-size: 1rem; }
.videocta div span { font-size: .85rem; color: var(--gray); }

/* footer */
footer.site {
  margin-top: 60px; border-top: 3px solid var(--ink); padding: 30px 0 44px;
  font-size: .85rem; color: #444;
}
footer.site .cols { display: flex; gap: 40px; flex-wrap: wrap; justify-content: space-between; }
footer.site a { color: var(--ink); }
footer.site .disclaimer { margin-top: 18px; color: var(--gray); max-width: 720px; }

@media (max-width: 620px) {
  nav.main a { margin-left: 12px; font-size: .88rem; }
  .hero { padding: 44px 0 30px; }
}