/* A quiet reading page: paper background, dark ink and green links.
   System fonts avoid external requests; article rows keep prose in reading order.
   ENERGY 1 / RHYTHM 1 / MOTION 1. */
:root{color-scheme:light;--paper:#f6f4ed;--ink:#26342d;--muted:#556157;--accent:#315e43;--line:#cdd3c8}
*{box-sizing:border-box}
html{scroll-padding-top:24px}
body{margin:0;background:var(--paper);color:var(--ink);font-family:-apple-system,BlinkMacSystemFont,"Segoe UI","Microsoft YaHei","PingFang SC",sans-serif;font-size:17px;line-height:1.85}
a{color:var(--accent);text-underline-offset:5px;text-decoration-thickness:1px}
a:hover{text-decoration-thickness:2px}
a:focus-visible{outline:3px solid var(--accent);outline-offset:5px;border-radius:2px}
.page{width:min(960px,100% - 80px);margin:auto}
.masthead{display:flex;align-items:center;justify-content:space-between;gap:24px;padding:29px 0;border-bottom:1px solid var(--line)}
.wordmark{font:700 32px/1.4 Georgia,"Times New Roman",serif;color:var(--ink);text-decoration:none}
.wordmark span{color:var(--accent)}
nav{display:flex;gap:26px}
nav a{display:inline-flex;align-items:center;min-height:44px;font-size:15px;text-decoration:none}
.intro{padding:78px 0 76px;max-width:720px}
.intro-label{margin:0 0 21px;font-size:15px;color:var(--muted)}
h1{margin:0;font-family:Georgia,"Songti SC","Noto Serif CJK SC","SimSun",serif;font-size:clamp(42px,6vw,66px);font-weight:600;line-height:1.3;letter-spacing:-1px}
.lead{margin:26px 0 18px;color:var(--muted);font-size:18px;line-height:1.9}
.read-link{display:inline-flex;align-items:center;min-height:44px;font-size:15px}
.notes{border-top:1px solid var(--line)}
article{display:grid;grid-template-columns:155px minmax(0,1fr);gap:44px;padding:46px 0;border-bottom:1px solid var(--line)}
.article-label{margin:4px 0 0;color:var(--muted);font-size:14px}
h2{font-size:26px;line-height:1.5;font-weight:600;letter-spacing:-.3px;margin:0 0 18px}
.article-copy p{margin:0 0 16px}
.article-copy p:last-child{margin-bottom:0}
.calculation{display:flex;align-items:baseline;flex-wrap:wrap;gap:17px;margin:23px 0 14px;padding:19px 0;border-top:1px solid var(--line);border-bottom:1px solid var(--line);font-variant-numeric:tabular-nums;font-size:22px;line-height:1.6}
.calculation strong{font-weight:600;color:var(--accent)}
.operator{color:var(--muted);font-size:17px}
.caption{font-size:14px;color:var(--muted)}
.about{max-width:660px;padding:52px 0 62px}
.about h2{font-size:21px;margin-bottom:13px}
.about p{margin:0 0 15px;color:var(--muted);font-size:16px}
.about a{display:inline-flex;align-items:center;min-height:44px;font-size:14px}
footer{border-top:1px solid var(--line);padding:22px 0 34px;display:flex;gap:12px;flex-wrap:wrap;justify-content:space-between;color:var(--muted);font-size:13px;overflow-wrap:anywhere}
.skip{position:absolute;left:20px;top:-100px;background:var(--paper);padding:8px 12px;z-index:1}
.skip:focus{top:10px}
.error{padding:70px 0;max-width:650px;min-height:65vh}
.error h1{font-size:48px}
.error p{color:var(--muted)}
@media(max-width:640px){
 .page{width:calc(100% - 40px)}
 .masthead{padding:20px 0;gap:16px}
 .wordmark{font-size:29px}
 nav{gap:18px}
 nav a{font-size:14px}
 .intro{padding:51px 0 48px}
 h1{font-size:42px}
 .lead{font-size:16px;margin-top:22px}
 .wide-only{display:none}
 article{grid-template-columns:minmax(0,1fr);gap:12px;padding:31px 0}
 h2{font-size:23px}
 body{font-size:16px}
 .calculation{font-size:20px;gap:12px}
 .about{padding:37px 0 42px}
 footer{display:block}
 footer span{display:block}
}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}}