/* elearn.ahermawan.site, open electrochemistry lessons */
:root{--bg:#FFFFFF;--alt:#EAF3EC;--ink:#0F2A1D;--ink2:#4B6156;--green:#1F7A4D;--green-d:#17603C;--amber:#E9A23B;--amber-l:#FCF1DC;--line:#D9E4DC;--red:#B4442F;--red-l:#F8E5E0}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){--bg:#FFFFFF;--ink:#0F2A1D}}
:root[data-theme="dark"]{--bg:#FFFFFF;--ink:#0F2A1D}
*,*::before,*::after{box-sizing:border-box}
[hidden]{display:none !important}
html{-webkit-text-size-adjust:100%}
body{margin:0;background:var(--bg);color:var(--ink);font-family:Manrope,"Segoe UI",Helvetica,Arial,sans-serif;font-size:18px;line-height:1.6;-webkit-font-smoothing:antialiased}
img,svg{max-width:100%;height:auto;display:block}
a{color:var(--green);text-decoration:none}
a:hover{text-decoration:underline}
a:focus-visible,button:focus-visible,input:focus-visible,select:focus-visible,textarea:focus-visible{outline:3px solid var(--amber);outline-offset:2px}
h1,h2,h3,h4{font-weight:700;margin:0;letter-spacing:-0.02em}
h1{font-size:clamp(34px,5vw,52px);line-height:1.1}
h2{font-size:clamp(26px,3.2vw,34px);line-height:1.2;margin-top:56px}
h3{font-size:clamp(20px,2vw,22px);line-height:1.3;letter-spacing:-0.01em;margin-top:32px}
h4{font-size:17px;letter-spacing:0}
p{margin:14px 0 0}
sub,sup{line-height:0}
.wrap{max-width:1160px;margin:0 auto;padding:0 24px}
.narrow{max-width:780px}
.skip{position:absolute;left:-9999px;top:0;background:#fff;color:var(--ink);padding:10px 14px;z-index:1000}
.skip:focus{left:8px;top:8px}
.muted{color:var(--ink2)}
.eyebrow{font-size:14px;font-weight:700;letter-spacing:.08em;text-transform:uppercase;color:var(--green);margin:0 0 10px}
.lead{font-size:clamp(17px,1.6vw,20px);color:var(--ink2);margin-top:20px;max-width:36em}

/* header and footer, matching ahermawan.site */
.site-head{position:sticky;top:0;z-index:50;background:#fff;border-bottom:1px solid var(--line)}
.site-head .wrap{display:flex;align-items:center;justify-content:space-between;gap:20px;padding-top:12px;padding-bottom:12px;flex-wrap:wrap}
.brand{display:flex;align-items:center;gap:12px;color:var(--ink)}
.brand:hover{text-decoration:none}
.brand img{height:42px;width:auto;flex:none}
.brand .bt{display:flex;flex-direction:column;line-height:1.25}
.brand .bn{font-size:15px;font-weight:700}
.brand .bs{font-size:13px;color:var(--ink2)}
.nav{display:flex;gap:20px;flex-wrap:wrap;font-size:15px}
.nav a{color:var(--ink)}
.nav a[aria-current]{color:var(--green);font-weight:700}
.nav-toggle{display:none;font:inherit;font-size:15px;font-weight:700;color:var(--ink);background:#fff;border:1.5px solid var(--ink);border-radius:8px;padding:8px 14px;min-height:44px;cursor:pointer}
.site-foot{background:var(--ink);color:#C9DACF;font-size:15px;padding:44px 0;margin-top:80px}
.site-foot .wrap{display:grid;grid-template-columns:minmax(0,1.4fr) repeat(2,minmax(0,1fr));gap:32px}
.site-foot b{color:#fff;display:block;margin-bottom:8px}
.site-foot a{color:#fff}
.site-foot p{margin:0}
.flogos{display:flex;align-items:center;gap:20px 28px;flex-wrap:wrap;margin-bottom:18px}
.flogos .fl-me{width:150px}.flogos .fl-brin{width:140px}

/* buttons */
.btn{display:inline-block;font-family:inherit;font-weight:700;font-size:16px;padding:12px 20px;border-radius:8px;border:1.5px solid transparent;cursor:pointer}
.btn:hover{text-decoration:none}
.btn-primary{background:var(--green);color:#fff}
.btn-primary:hover{background:var(--green-d)}
.btn-secondary{border-color:var(--ink);color:var(--ink);background:#fff}
.btn-secondary:hover{background:var(--alt)}
.actions{display:flex;gap:12px;flex-wrap:wrap;margin-top:26px}
.btn-s{font:inherit;font-size:14px;font-weight:700;color:var(--green);background:#fff;border:1.5px solid var(--green);border-radius:8px;padding:7px 12px;min-height:38px;cursor:pointer}
.btn-s:hover{background:var(--alt)}
.btn-s.ghost{color:var(--ink2);border-color:var(--line)}
.chip{font:inherit;font-size:14px;font-weight:700;color:var(--ink);background:var(--alt);border:1.5px solid transparent;border-radius:999px;padding:6px 14px;min-height:36px;cursor:pointer}
.chip:hover{border-color:var(--green)}

/* bands, hero, cards */
.band{padding:clamp(48px,7vw,84px) 0}
.band-alt{background:var(--alt)}
.hero{padding:clamp(44px,6vw,76px) 0 clamp(36px,5vw,60px)}
.hero .wrap{display:grid;grid-template-columns:minmax(0,1.1fr) minmax(0,1fr);gap:44px;align-items:center}
.hero-art svg{width:100%;height:auto}
.grid3{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:24px;margin-top:32px}
.grid2{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:24px;margin-top:32px}
.card{border:1px solid var(--line);border-radius:16px;padding:24px;background:#fff;display:flex;flex-direction:column}
.card h3{margin-top:0}
.card p{color:var(--ink2);font-size:16px;margin-top:8px}
.card .go{margin-top:auto;padding-top:16px;font-weight:700;font-size:16px}
.card .num{font-size:13px;font-weight:700;color:var(--green);letter-spacing:.06em;text-transform:uppercase}
.card .art{background:var(--alt);border-radius:12px;margin:-8px -8px 16px;padding:10px}
.card .art svg{width:100%;height:auto}
.card.lock{background:#FAFCFA}
.badge{display:inline-block;font-size:12px;font-weight:700;letter-spacing:.04em;padding:3px 9px;border-radius:999px;background:var(--alt);color:var(--green);vertical-align:middle}
.badge.amber{background:var(--amber-l);color:#8A5A12}
.badge.done{background:var(--green);color:#fff}
.prog{font-size:13px;font-weight:700;color:var(--ink2);margin-top:10px}

/* lesson body */
.lesson-head{padding:44px 0 8px;border-bottom:1px solid var(--line)}
.lesson-head .meta{display:flex;gap:16px;flex-wrap:wrap;color:var(--ink2);font-size:15px;margin-top:16px}
.crumbs{font-size:14px;color:var(--ink2)}
.crumbs a{color:var(--ink2)}
.lesson{display:grid;grid-template-columns:220px minmax(0,1fr);gap:48px;padding-top:36px}
.toc{position:sticky;top:96px;align-self:start;font-size:14px;border-left:2px solid var(--line);padding-left:14px}
.toc b{display:block;font-size:13px;letter-spacing:.06em;text-transform:uppercase;color:var(--ink2);margin-bottom:8px}
.toc a{display:block;color:var(--ink);padding:4px 0}
.toc a:hover{color:var(--green)}
.prose{max-width:760px}
.prose > h2:first-child{margin-top:0}
.prose ul,.prose ol{padding-left:22px;margin:14px 0 0}
.prose li{margin:6px 0}
.prose table{border-collapse:collapse;width:100%;margin-top:18px;font-size:16px}
.prose th,.prose td{border-bottom:1px solid var(--line);padding:9px 10px;text-align:left;vertical-align:top}
.prose th{background:var(--alt);font-size:14px}
.tablewrap{overflow-x:auto;-webkit-overflow-scrolling:touch}
.key{background:var(--alt);border-radius:14px;padding:18px 22px;margin-top:22px}
.key b:first-child{display:block;margin-bottom:4px}
.warn{background:var(--amber-l);border-left:4px solid var(--amber);border-radius:0 12px 12px 0;padding:14px 18px;margin-top:22px;font-size:16px}
.eq{font-family:"Cambria Math","STIX Two Math","Times New Roman",serif;font-size:20px;background:#fff;border:1px solid var(--line);border-radius:12px;padding:14px 18px;margin-top:18px;overflow-x:auto;white-space:nowrap}
.eq small{font-family:Manrope,system-ui,sans-serif;font-size:14px;color:var(--ink2);display:block;white-space:normal;margin-top:6px}
figure{margin:24px 0 0}
figure svg{width:100%;height:auto;background:var(--alt);border-radius:14px}
figcaption{font-size:14px;color:var(--ink2);margin-top:8px}
.refs{font-size:15px;color:var(--ink2)}
.refs li{margin:8px 0}
.next{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap;border-top:1px solid var(--line);margin-top:48px;padding-top:24px;font-weight:700}

/* simulator */
.sim{border:1px solid var(--line);border-radius:18px;padding:18px;background:#fff;margin-top:24px}
.sim-presets{display:flex;gap:8px;flex-wrap:wrap;margin-bottom:14px}
.sim-grid{display:grid;grid-template-columns:300px minmax(0,1fr);gap:22px}
.sim-panel{display:flex;flex-direction:column;gap:12px}
.ctl label{display:flex;justify-content:space-between;align-items:baseline;gap:8px;font-size:14px;font-weight:700}
.ctl output{font-weight:700;color:var(--green);white-space:nowrap;font-size:14px}
.ctl small{display:block;color:var(--ink2);font-size:12.5px;line-height:1.4;margin-top:2px}
.ctl input[type=range]{width:100%;accent-color:var(--green);margin:6px 0 0;height:28px}
.chk{display:flex !important;justify-content:flex-start !important;gap:8px;align-items:center !important;font-weight:400 !important;cursor:pointer}
.chk input{accent-color:var(--green);width:18px;height:18px}
.win-ctl{display:flex;flex-direction:column;gap:12px}
.sel-row{display:grid;grid-template-columns:repeat(auto-fit,minmax(110px,1fr));gap:10px}
.fld-s label{display:block;font-size:13px;font-weight:700;margin-bottom:4px}
.fld-s select,.fld-s input{width:100%;font:inherit;font-size:14px;color:var(--ink);background:#fff;border:1.5px solid var(--line);border-radius:8px;padding:7px 8px;min-height:38px}
.plot-box{background:#fff}
canvas.plot{width:100%;height:380px;display:block;touch-action:pan-y}
canvas.plot.sm{height:280px}
.sim-tools{display:flex;gap:8px;flex-wrap:wrap;margin-top:10px}
.readout{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px;margin-top:14px}
.ro{background:var(--alt);border-radius:10px;padding:9px 12px;display:flex;flex-direction:column;font-size:13.5px;line-height:1.35}
.ro span{color:var(--ink2)}
.ro b{font-size:16px;margin-top:3px}
.ro-wide{grid-column:1 / -1}
.reg-reversible{background:#DCEFE2}
.reg-quasireversible{background:var(--amber-l)}
.reg-irreversible{background:var(--red-l)}
.note{font-size:14px;color:var(--ink2);margin:6px 0 0}
.study{border-top:1px solid var(--line);margin-top:18px;padding-top:16px}
.study .muted{font-size:14px;margin-top:4px}
.two-plots{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px;margin-top:10px}
.scrub{display:flex;gap:12px;align-items:center;margin-top:10px;flex-wrap:wrap}
.scrub input{flex:1;min-width:160px;accent-color:var(--green)}
.scrub output{font-size:14px;font-weight:700;color:var(--ink2);min-width:170px}

/* EIS */
.eis-circ{background:var(--alt);border-radius:12px;padding:10px 12px;margin-bottom:6px}
.eis-circ svg{width:100%;height:auto}
.eis-plots{display:grid;grid-template-columns:minmax(0,1.1fr) minmax(0,1fr);gap:14px}
.eis-plots .bode{display:flex;flex-direction:column;gap:10px}
.eis-plots canvas.plot{height:360px}
.eis-plots .bode canvas.plot{height:175px}

/* calculators */
.calc{border:1px solid var(--line);border-radius:18px;padding:22px;background:#fff;margin-top:24px}
.calc h3{margin-top:0}
.calc .row{display:grid;grid-template-columns:repeat(auto-fit,minmax(150px,1fr));gap:12px;margin-top:14px}
.calc label{display:block;font-size:13.5px;font-weight:700}
.calc input,.calc select,.calc textarea{display:block;width:100%;margin-top:5px;font:inherit;font-size:15px;color:var(--ink);background:#fff;border:1.5px solid var(--line);border-radius:8px;padding:8px 10px;min-height:42px}
.calc textarea{font-family:ui-monospace,Menlo,Consolas,monospace;font-size:14px;min-height:150px;resize:vertical}
.calc .res{display:grid;grid-template-columns:repeat(auto-fit,minmax(180px,1fr));gap:8px;margin-top:16px}
.calc .formula{font-size:14px;color:var(--ink2);margin-top:12px}
.calc .err{color:var(--red);font-size:14px;margin-top:10px;font-weight:700}
.calc canvas.plot{height:300px;margin-top:14px}
.calc table{border-collapse:collapse;width:100%;font-size:15px;margin-top:14px}
.calc th,.calc td{border-bottom:1px solid var(--line);padding:7px 8px;text-align:left}
.calc td input{margin-top:0;min-height:36px;padding:6px 8px}
.calc-nav{display:flex;gap:8px;flex-wrap:wrap;margin-top:24px}

/* quiz */
.quiz{border:2px solid var(--green);border-radius:18px;padding:22px;margin-top:28px;background:#fff}
.quiz h3{margin-top:0}
.q{border-top:1px solid var(--line);padding:18px 0 4px}
.q:first-of-type{border-top:0}
.q p.qt{font-weight:700;margin:0}
.q .opts{display:grid;gap:8px;margin-top:12px}
.q .opt{display:flex;gap:10px;align-items:flex-start;text-align:left;font:inherit;font-size:16px;color:var(--ink);background:#fff;border:1.5px solid var(--line);border-radius:10px;padding:10px 12px;cursor:pointer;width:100%}
.q .opt:hover:not([disabled]){border-color:var(--green)}
.q .opt .lt{font-weight:700;color:var(--ink2);min-width:20px}
.q .opt.right{border-color:var(--green);background:#DCEFE2}
.q .opt.wrong{border-color:var(--red);background:var(--red-l)}
.q .opt[disabled]{cursor:default}
.q .fb{font-size:15px;margin-top:10px;padding:10px 12px;border-radius:10px;background:var(--alt)}
.q .fb b{display:block}
.score{display:flex;gap:14px;align-items:center;flex-wrap:wrap;border-top:1px solid var(--line);margin-top:14px;padding-top:16px;font-weight:700}

@media (max-width:980px){
  .sim-grid{grid-template-columns:minmax(0,1fr)}
  .eis-plots{grid-template-columns:minmax(0,1fr)}
  .lesson{grid-template-columns:minmax(0,1fr);gap:0}
  .toc{display:none}
  .grid3{grid-template-columns:repeat(2,minmax(0,1fr))}
}
@media (max-width:820px){
  .nav-toggle{display:inline-block}
  .site-head .nav{display:none;flex-direction:column;gap:0;width:100%;font-size:16px}
  .site-head.nav-open .nav{display:flex}
  .site-head .nav a{padding:12px 0;border-top:1px solid var(--line)}
  .hero .wrap,.site-foot .wrap,.grid2,.grid3{grid-template-columns:minmax(0,1fr)}
  .two-plots{grid-template-columns:minmax(0,1fr)}
  .readout{grid-template-columns:minmax(0,1fr)}
  canvas.plot{height:300px}
  .eis-plots canvas.plot{height:300px}
  .eis-plots .bode canvas.plot{height:200px}
  .sim,.calc,.quiz{padding:14px;border-radius:14px}
  .wrap{padding:0 16px}
}
@media (prefers-reduced-motion:reduce){*{animation:none !important;transition:none !important}}
.tip{position:absolute;background:#fff;border:1px solid var(--line);border-radius:8px;padding:6px 10px;font-size:13px;line-height:1.4;box-shadow:0 4px 14px rgba(15,42,29,.12);pointer-events:none;min-width:110px}
.chip[aria-pressed="true"]{border-color:var(--green);background:#fff}
.grid2 .card .art svg{max-height:150px;width:auto;margin:0 auto}
.prose .sim-grid{grid-template-columns:minmax(0,1fr)}
.prose .sim-panel{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 24px}
.prose .sim-panel .ctl-win,.prose .sim-panel .win-ctl{grid-column:1 / -1}
.prose .sim-panel .win-ctl{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 24px}
@media (max-width:820px){.prose .sim-panel,.prose .sim-panel .win-ctl{grid-template-columns:minmax(0,1fr)}}
.calc .row > div{display:flex;flex-direction:column;justify-content:flex-end}