/* Battery Research Notes. Fonts are self-hosted (no requests to Google). */
@font-face{font-family:"Source Serif 4";font-weight:400;font-style:normal;font-display:swap;src:url("fonts/source-serif-4-latin-400-normal.woff2") format("woff2")}
@font-face{font-family:"Source Serif 4";font-weight:400;font-style:italic;font-display:swap;src:url("fonts/source-serif-4-latin-400-italic.woff2") format("woff2")}
@font-face{font-family:"Source Serif 4";font-weight:600;font-style:normal;font-display:swap;src:url("fonts/source-serif-4-latin-600-normal.woff2") format("woff2")}
@font-face{font-family:"Schibsted Grotesk";font-weight:500;font-style:normal;font-display:swap;src:url("fonts/schibsted-grotesk-latin-500-normal.woff2") format("woff2")}
@font-face{font-family:"Schibsted Grotesk";font-weight:700;font-style:normal;font-display:swap;src:url("fonts/schibsted-grotesk-latin-700-normal.woff2") format("woff2")}

:root{
  --bg:#F2F4F5; --ink:#16212B; --muted:#52606B; --line:#C9D1D6; --accent:#343A8C; --amber:#9A5B00;
  --al:#B9C3CA; --cu:#C07A3C; --sep:#E3E8EB; --pore:#B4BFC6;
  --cat:#343A8C; --cat-bg:#D8DBEE; --an:#3A3F47; --an-bg:#D9DDE1; --ion:#F2B01E; --ion-edge:#16212B;
  --sans:"Schibsted Grotesk",system-ui,-apple-system,"Segoe UI",sans-serif;
  --serif:"Source Serif 4",Georgia,"Times New Roman",serif;
}
@media (prefers-color-scheme:dark){:root{
  --bg:#0F161C; --ink:#E6ECF0; --muted:#98A5AF; --line:#26323B; --accent:#A9B0FF; --amber:#E0A040;
  --al:#566570; --cu:#C9884A; --sep:#1B252D; --pore:#33424D;
  --cat:#7C84F0; --cat-bg:#1A2040; --an:#8A949E; --an-bg:#1F272E; --ion:#FFD166; --ion-edge:#0F161C;
}}

*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font:400 18px/1.7 var(--serif);text-rendering:optimizeLegibility}
.wrap{max-width:720px;margin:0 auto;padding:0 20px}
a{color:var(--accent);text-underline-offset:.18em;text-decoration-thickness:1px}
a:hover{text-decoration-thickness:2px}
:focus-visible{outline:2px solid var(--accent);outline-offset:3px;border-radius:2px}
.skip{position:absolute;left:-999px;top:8px;background:var(--ink);color:var(--bg);padding:8px 12px;z-index:9}
.skip:focus{left:8px}

/* header */
.top{position:sticky;top:0;z-index:5;background:var(--bg);border-bottom:1px solid var(--line)}
.top .left{display:flex;align-items:center;gap:14px;min-width:0}
.soc{display:inline-flex;align-items:center;gap:6px;font:500 12px var(--sans);color:var(--muted);font-variant-numeric:tabular-nums}
.cell{position:relative;display:inline-block;width:24px;height:11px;border:1.5px solid var(--muted);border-radius:3px;padding:1px}
.cell::after{content:"";position:absolute;right:-4.5px;top:2px;width:2.5px;height:4px;background:var(--muted);border-radius:0 1px 1px 0}
.cell i{display:block;height:100%;width:100%;background:var(--accent);transform-origin:left;transform:scaleX(0);border-radius:1px}
#soc-pct{min-width:2.6em}
.top .wrap{display:flex;justify-content:space-between;align-items:baseline;gap:16px;padding-top:18px;padding-bottom:18px}
.brand{font:700 17px/1.2 var(--sans);color:var(--ink);text-decoration:none;letter-spacing:-.01em}
nav{font:500 15px var(--sans)}
nav a{margin-left:20px;color:var(--muted);text-decoration:none}
nav a:hover{color:var(--accent);text-decoration:underline}

/* masthead: electrode cross-section, the one bold element */
.stack{display:block;width:100%;height:162px}
.stack text{font:500 10.5px var(--sans);fill:var(--muted)}
.stack .al{fill:var(--al)} .stack .cu{fill:var(--cu)} .stack .sep{fill:var(--sep)} .stack .pore{fill:var(--pore)}
.stack .cat-bg{fill:var(--cat-bg)} .stack .cat{fill:var(--cat)}
.stack .an-bg{fill:var(--an-bg)} .stack .an{fill:var(--an)}
.stack .ion{fill:var(--ion);stroke:var(--ion-edge);stroke-width:.8}
.cellctl{display:flex;justify-content:space-between;align-items:center;gap:16px;padding-top:12px;padding-bottom:0}
.cellctl p{margin:0;font:400 14px/1.45 var(--sans);color:var(--muted);max-width:42em}
.seg{display:none;flex:none;border:1px solid var(--ink);border-radius:4px;overflow:hidden}
.js .seg{display:inline-flex}
.seg button{font:700 14px var(--sans);padding:7px 14px;border:0;background:transparent;color:var(--ink);cursor:pointer}
.seg button+button{border-left:1px solid var(--ink)}
.seg button[aria-pressed="true"]{background:var(--ink);color:var(--bg)}

/* home */
.intro{padding:40px 0 8px}
.intro h1{font:700 clamp(38px,8vw,60px)/1.02 var(--sans);letter-spacing:-.03em;margin:0 0 14px}
.intro p{margin:0;max-width:34em;color:var(--muted);font-size:20px;line-height:1.55}
.featured{padding:44px 0 36px}
.featured time,.post time,.list time{font:500 14px var(--sans);color:var(--muted);font-variant-numeric:tabular-nums}
.featured h2{font:700 clamp(28px,5vw,38px)/1.15 var(--sans);letter-spacing:-.02em;margin:6px 0 12px}
.featured h2 a{color:var(--ink);text-decoration:none}
.featured h2 a:hover{color:var(--accent);text-decoration:underline;text-decoration-thickness:2px}
.featured p{margin:0 0 12px;max-width:36em}
.topics{display:flex;flex-wrap:wrap;gap:4px 16px;margin:0;font:500 14px var(--sans);color:var(--muted)}
.topics .draft{color:var(--amber);font-weight:700}
.topics span{white-space:nowrap}
.sw{display:inline-block;width:9px;height:9px;border-radius:2px;background:var(--c);margin-right:6px}
.vh{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}

/* all notes: discharge curve, topic filters, list */
.notes{padding:8px 0 24px}
.notes h2{font:700 22px var(--sans);letter-spacing:-.01em;margin:0 0 12px}
.curve{margin:0 0 16px}
.curve svg{display:block;width:100%;height:auto;overflow:visible}
.curve text{font:500 11px var(--sans);fill:var(--muted)}
.curve .grid{stroke:var(--line);stroke-width:1}
.curve .path{fill:none;stroke:var(--ink);stroke-width:2;stroke-linejoin:round}
.curve .path.rest{stroke:var(--muted);stroke-width:1.5;stroke-dasharray:3 5}
.curve .pt{stroke:var(--bg);stroke-width:2.5;cursor:pointer}
.curve .pt.dim{opacity:.15}
.curve a:hover .pt{stroke:var(--ink)}
.curve figcaption{font:400 13px/1.45 var(--sans);color:var(--muted);margin-top:6px;max-width:44em}
.chips{display:none;flex-wrap:wrap;gap:8px;margin:0 0 6px}
.js .chips{display:flex}
.chips button{font:500 14px var(--sans);display:inline-flex;align-items:center;padding:6px 11px;border:1px solid var(--line);border-radius:4px;background:transparent;color:var(--ink);cursor:pointer}
.chips button:hover{border-color:var(--muted)}
.chips button[aria-pressed="true"]{border-color:var(--ink);background:var(--an-bg)}
.list{list-style:none;margin:0;padding:0;border-top:1px solid var(--line)}
.list li{display:grid;grid-template-columns:96px 1fr;gap:12px;padding:12px 0;border-bottom:1px solid var(--line)}
.list li[hidden]{display:none}
.list a{font:500 18px/1.4 var(--sans);color:var(--ink);text-decoration:none}
.list a:hover{color:var(--accent);text-decoration:underline}

/* post */
.post{padding:44px 0 8px}
.post header{margin-bottom:28px}
.post h1{font:700 clamp(30px,6vw,44px)/1.1 var(--sans);letter-spacing:-.025em;margin:8px 0 14px}
.prose{max-width:66ch}
.prose p{margin:0 0 1.15em}
.prose h2{font:700 24px/1.25 var(--sans);letter-spacing:-.01em;margin:2.1em 0 .5em}
.prose h3{font:700 19px/1.3 var(--sans);margin:1.6em 0 .4em}
.prose ul{padding-left:1.2em;margin:0 0 1.2em}
.prose li{margin-bottom:.7em;padding-left:.2em}
.prose li::marker{color:var(--accent)}
.prose strong{font-weight:600}
code{font-size:.9em;background:var(--an-bg);padding:.1em .35em;border-radius:3px}

/* email signup: a plain band, not a card */
.subscribe{margin:36px 0;padding:22px 0;border-top:2px solid var(--ink)}
.subscribe h2{font:700 21px/1.25 var(--sans);letter-spacing:-.01em;margin:0 0 4px}
.subscribe p{margin:0 0 14px;color:var(--muted);font-size:16px;line-height:1.5;max-width:34em}
.subscribe form{display:flex;gap:10px;flex-wrap:wrap}
.subscribe input{flex:1 1 240px;min-width:0;padding:11px 12px;font:500 16px var(--sans);border:1px solid var(--muted);border-radius:3px;background:transparent;color:var(--ink)}
.subscribe input::placeholder{color:var(--muted)}
.subscribe button{padding:11px 20px;font:700 16px var(--sans);border:0;border-radius:3px;background:var(--accent);color:var(--bg);cursor:pointer}
.subscribe button:hover{filter:brightness(1.12)}

footer{margin-top:24px;padding-bottom:36px;color:var(--muted);font:400 14px var(--sans)}
footer p{margin:0;padding-top:18px;border-top:1px solid var(--line)}
.quote{margin:0 0 20px;padding:0 0 0 14px;border-left:3px solid var(--accent);font:italic 400 19px/1.5 var(--serif);color:var(--ink);max-width:30em}

@media (max-width:520px){
  .cellctl{flex-direction:column;align-items:flex-start;gap:10px}
  body{font-size:17px}
  .list li{grid-template-columns:1fr;gap:0}
  nav a{margin-left:14px}
}