/* Balance It Yourself.
   Layout: Roji brand header, two tabs, then choices on the left and the working area on the right (stacked on phones).
   The equation reads like a real one: each big number sits in front of its formula with a small stepper. */
:root{
  --navy:#1D5B8D; --sky:#0B7CC9; --green:#3CC47C; --green-ink:#1E8A52;
  --bg:#EEF5FB; --surface:#FFFFFF; --ink:#16324A; --muted:#557089; --line:#CFE0EE; --field:#F7FBFE; --tint:#E3EFF9;
  --on-navy:#FFFFFF; --warn-bg:#FFF1CC; --warn-ink:#7A5400; --ok-bg:#DDF5E8; --ok-ink:#15693F;
  --left:#0B7CC9; --right:#E39A1B; --right-line:#9A6400;
  --title-fill:#0B7CC9; --title-stroke:#12344F;
  --shadow:0 1px 0 #d7e6f2, 0 10px 30px -18px rgba(29,91,141,.45);
  --f-display:"Luckiest Guy","Arial Rounded MT Bold","Trebuchet MS",sans-serif;
  --f-body:"Nunito",system-ui,-apple-system,"Segoe UI",sans-serif;
  color-scheme:light;
}
@media (prefers-color-scheme: dark){:root:not([data-theme="light"]){
  --bg:#0E1B27; --surface:#15283A; --ink:#E6F0F8; --muted:#9BB3C8; --line:#27425A; --field:#10202F; --tint:#1B3247;
  --navy:#5CADE2; --sky:#5CADE2; --green-ink:#5FD897; --on-navy:#06121C;
  --warn-bg:#3B3013; --warn-ink:#F4CF6E; --ok-bg:#153B2A; --ok-ink:#7FE3AE;
  --left:#5CADE2; --right:#E9B04A; --right-line:#F4CF6E;
  --title-fill:#5CADE2; --title-stroke:#06121C; --shadow:0 12px 30px -20px rgba(0,0,0,.8); color-scheme:dark}}
:root[data-theme="dark"]{
  --bg:#0E1B27; --surface:#15283A; --ink:#E6F0F8; --muted:#9BB3C8; --line:#27425A; --field:#10202F; --tint:#1B3247;
  --navy:#5CADE2; --sky:#5CADE2; --green-ink:#5FD897; --on-navy:#06121C;
  --warn-bg:#3B3013; --warn-ink:#F4CF6E; --ok-bg:#153B2A; --ok-ink:#7FE3AE;
  --left:#5CADE2; --right:#E9B04A; --right-line:#F4CF6E;
  --title-fill:#5CADE2; --title-stroke:#06121C; --shadow:0 12px 30px -20px rgba(0,0,0,.8); color-scheme:dark}

*{box-sizing:border-box}
[hidden]{display:none!important}
body{margin:0;background:var(--bg);color:var(--ink);font-family:var(--f-body);font-size:16px;line-height:1.5;-webkit-text-size-adjust:100%}
.wrap{max-width:1180px;margin:0 auto;padding-inline:clamp(16px,3vw,32px);padding-block:12px 40px}
button,input,select{font-family:inherit}
:focus-visible{outline:3px solid var(--green);outline-offset:2px}
p{margin:0}
sub{font-size:.68em;line-height:0;vertical-align:-.28em;font-variant-numeric:tabular-nums}
.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip-path:inset(50%);white-space:nowrap}
.f{white-space:nowrap}

/* ---------- brand header (same on every Roji tool) ---------- */
.brandbar{display:flex;justify-content:space-between;align-items:center;gap:12px;font-weight:800;color:var(--navy);font-size:.9rem}
.brandbar a{color:inherit;text-decoration:none}
.brandbar .kit{letter-spacing:.08em;text-transform:uppercase;font-size:.72rem;color:var(--muted)}
.hero{display:flex;align-items:center;margin-block:4px 10px}
.hero-text{flex:1;min-width:0;padding-bottom:clamp(8px,2vw,20px)}
.eyebrow{font-weight:800;color:var(--green-ink);letter-spacing:.08em;text-transform:uppercase;font-size:.78rem}
h1{font-family:var(--f-display);font-weight:400;font-size:clamp(2.1rem,6vw,3.8rem);line-height:.95;margin:4px 0 10px;
  color:var(--title-fill);-webkit-text-stroke:2px var(--title-stroke);paint-order:stroke fill;letter-spacing:.01em;text-wrap:balance;text-shadow:0 3px 0 var(--title-stroke)}
h1 .grades{display:inline-block;font-size:.5em;line-height:1.1;-webkit-text-stroke:1.5px var(--title-stroke);text-shadow:0 2px 0 var(--title-stroke);white-space:nowrap}
.tagline{color:var(--muted);font-weight:700;max-width:52ch}
.roji{flex:0 0 auto;width:clamp(110px,20vw,200px);display:block}
.roji img{width:100%;height:auto;display:block;filter:drop-shadow(0 8px 12px rgba(18,52,79,.18))}

/* ---------- tabs ---------- */
.tabs{display:flex;gap:8px;margin-bottom:16px;flex-wrap:wrap}
.tabs button{flex:1 1 150px;font-family:var(--f-display);font-size:1.15rem;letter-spacing:.02em;line-height:1.1;padding:.7em .8em .5em;min-height:52px;
  border:2px solid var(--navy);border-radius:14px;background:var(--surface);color:var(--navy);cursor:pointer}
.tabs button[aria-selected="true"]{background:var(--navy);color:var(--on-navy)}

/* ---------- layout ---------- */
.app{display:grid;grid-template-columns:minmax(0,340px) minmax(0,1fr);gap:20px;align-items:start}
@media (max-width:900px){.app{grid-template-columns:minmax(0,1fr)}}
.panel{background:var(--surface);border-radius:18px;box-shadow:var(--shadow);padding:6px 20px 20px;min-width:0}
.stage{display:grid;gap:14px;min-width:0}
.stage > .panel{padding-top:16px;display:grid;gap:12px}
.grp{padding-top:14px;display:grid;gap:10px}
.grp+.grp{border-top:2px dashed var(--line);margin-top:16px}
.grp h2,.rtitle{font-size:.78rem;text-transform:uppercase;letter-spacing:.08em;color:var(--green-ink);margin:0;font-weight:800}
label{display:grid;gap:4px;font-size:.85rem;font-weight:800;color:var(--muted)}
.hint{font-weight:600;font-size:.82rem;color:var(--muted)}
.lbl{font-size:.85rem;font-weight:800;color:var(--muted);margin-bottom:6px}
input[type="text"],select{font-size:1.05rem;font-weight:800;color:var(--ink);background:var(--field);border:2px solid var(--line);border-radius:10px;padding:9px 10px;width:100%;min-width:0;min-height:44px}
input:focus,select:focus{border-color:var(--sky)}
input::placeholder{color:var(--muted);opacity:.75;font-weight:700}
.seg{display:flex;flex-wrap:wrap;gap:6px}
.seg button{font-size:.9rem;font-weight:800;border:2px solid var(--line);background:var(--surface);color:var(--ink);border-radius:999px;padding:8px 13px;min-height:44px;min-width:44px;cursor:pointer}
.seg button[aria-pressed="true"]{background:var(--navy);color:var(--on-navy);border-color:var(--navy)}
.check{display:flex;align-items:center;gap:10px;font-weight:700;color:var(--ink);font-size:.95rem}
.check input{width:24px;height:24px;flex:none;accent-color:var(--green)}
.btn{display:inline-flex;align-items:center;justify-content:center;font-size:.95rem;font-weight:800;border:2px solid var(--navy);background:var(--navy);color:var(--on-navy);
  border-radius:12px;padding:9px 16px;min-height:44px;cursor:pointer;text-decoration:none}
.btn.ghost{background:transparent;color:var(--navy)}
.btn.small{font-size:.88rem;padding:6px 12px}
.btn:disabled{opacity:.4;cursor:default}
.actions{display:flex;flex-wrap:wrap;gap:8px}
.feedback{border-radius:12px;padding:10px 14px;font-weight:800;background:var(--warn-bg);color:var(--warn-ink)}
.feedback.good{background:var(--ok-bg);color:var(--ok-ink)}
.feedback.plain{background:var(--tint);color:var(--ink)}
.note{font-weight:700;font-size:.9rem;color:var(--muted);background:var(--tint);border-radius:10px;padding:8px 12px}

/* ---------- the equation ---------- */
.eqhead{display:flex;align-items:baseline;justify-content:space-between;gap:10px;flex-wrap:wrap}
.eqname{margin:0;font-family:var(--f-display);font-weight:400;font-size:1.35rem;line-height:1.15;color:var(--navy);letter-spacing:.02em;padding-top:.1em;text-wrap:balance}
.tag{font-size:.72rem;font-weight:800;text-transform:uppercase;letter-spacing:.08em;color:var(--muted);border:2px solid var(--line);border-radius:999px;padding:2px 10px;white-space:nowrap}
.tag:empty{display:none}
.equation{display:flex;flex-wrap:wrap;align-items:center;gap:10px clamp(6px,1.4vw,12px);background:var(--tint);border-radius:16px;padding:14px clamp(8px,2vw,18px)}
.term{display:flex;align-items:center;gap:6px;min-width:0}
.stepper{display:grid;grid-template-rows:auto auto auto;gap:3px;flex:none;width:52px}
.stepper button{height:34px;border:2px solid var(--navy);background:var(--surface);color:var(--navy);border-radius:10px;font-size:1.25rem;font-weight:800;line-height:1;cursor:pointer;padding:0}
.stepper button.up{background:var(--navy);color:var(--on-navy)}
.stepper button:disabled{opacity:.35;cursor:default}
.stepper input{font-family:var(--f-display);font-weight:400;font-size:1.7rem;line-height:1;text-align:center;padding:.22em 0 0;height:46px;min-height:0;border-radius:10px;color:var(--navy);background:var(--surface);font-variant-numeric:tabular-nums}
.term .f{font-size:clamp(1.35rem,4.6vw,1.9rem);font-weight:800;letter-spacing:.01em}
.op{font-size:1.5rem;font-weight:800;color:var(--muted);flex:none;margin-right:2px}
.op.arrow{font-size:1.9rem;color:var(--ink);line-height:1}
.written{font-weight:800;font-size:1.05rem;overflow-wrap:anywhere}
.lbl-inline{font-size:.72rem;text-transform:uppercase;letter-spacing:.08em;color:var(--green-ink);margin-right:6px}
.written .f{white-space:normal}
.confirm{background:var(--tint);border-radius:12px;padding:10px 14px;display:grid;gap:8px;font-weight:700}

/* ---------- atom tally ---------- */
.tallyhead{display:flex;justify-content:space-between;align-items:center;gap:8px 16px;flex-wrap:wrap}
.legend{list-style:none;margin:0;padding:0;display:flex;flex-wrap:wrap;gap:4px 14px;font-size:.8rem;font-weight:700;color:var(--muted)}
.legend li{display:flex;align-items:center;gap:6px}
.swatch{width:14px;height:14px;border-radius:4px;flex:none}
.swatch.l{background:var(--left)}
.swatch.r{background:var(--right);border-radius:50%}
.tablewrap{overflow-x:auto;min-width:0}
table{border-collapse:collapse;width:100%;font-variant-numeric:tabular-nums}
th,td{padding:8px 6px;text-align:left;border-bottom:2px solid var(--line);vertical-align:middle}
thead th{font-size:.72rem;text-transform:uppercase;letter-spacing:.06em;color:var(--muted);font-weight:800;white-space:nowrap}
tbody tr:last-child > *{border-bottom:0}
.num{text-align:right}
.elcell b{font-size:1.2rem;font-weight:800}
.elcell span{display:block;font-size:.76rem;font-weight:700;color:var(--muted);line-height:1.1}
.tally td.num{font-family:var(--f-display);font-size:1.5rem;line-height:1;padding-top:.5em;color:var(--navy);width:3.2em}
.tally .barcol{width:42%;min-width:90px}
.bars{display:grid;grid-template-columns:1fr 1fr;gap:3px;align-items:center}
.bars i{display:block;height:16px;min-width:3px;transition:width .2s}
.bars .l{justify-self:end;background:var(--left);border-radius:5px 0 0 5px}
.bars .r{justify-self:start;background:var(--right);border-radius:0 8px 8px 0}
.match{font-weight:800;font-size:.9rem;white-space:nowrap}
.match.yes{color:var(--ok-ink)}
.match.no{color:var(--warn-ink)}
.match .mark{display:inline-flex;align-items:center;justify-content:center;width:1.5em;height:1.5em;border-radius:50%;margin-right:5px;font-size:.9em}
.match.yes .mark{background:var(--ok-bg)}
.match.no .mark{background:var(--warn-bg)}
tr.ok td.elcell b{color:var(--ok-ink)}
.counted summary{cursor:pointer;font-weight:800;color:var(--navy);font-size:.92rem}
.counted ul{margin:8px 0 0;padding:0;list-style:none;display:grid;gap:6px;font-weight:700;font-size:.95rem}
.counted li b{font-weight:800}
.counted .side{color:var(--muted);font-size:.78rem;text-transform:uppercase;letter-spacing:.06em;font-weight:800}

.bubble{background:var(--navy);color:var(--on-navy);border-radius:18px;padding:12px 18px 14px;font-weight:800;font-size:1.05rem;max-width:62ch}
.bubble .who{display:block;font-size:.72rem;letter-spacing:.08em;text-transform:uppercase;opacity:.85}
.masscard p{font-weight:700;max-width:62ch}
.masscard b{font-weight:800}

/* ---------- molar mass ---------- */
.formulacard{justify-items:start}
.bigformula{font-size:clamp(2rem,8vw,3.2rem);font-weight:800;line-height:1.2;overflow-wrap:anywhere;max-width:100%}
.bigformula .f{white-space:normal}
.total{font-family:var(--f-display);font-size:clamp(1.9rem,7vw,2.8rem);line-height:1;color:var(--navy);padding-top:.12em;font-variant-numeric:tabular-nums}
.total small{font-family:var(--f-body);font-weight:800;font-size:.42em;color:var(--muted);margin-left:.3em}
.guesscard input{max-width:260px;font-size:1.3rem}
.masstable td.num,.masstable tfoot td{font-weight:800}
.masstable tfoot th,.masstable tfoot td{border-bottom:0;border-top:3px solid var(--navy);font-weight:800;font-size:1.05rem;color:var(--navy)}
.masstable .unit{color:var(--muted);font-weight:700;font-size:.82em}
.hidden-val{color:var(--muted)}

.how{background:var(--surface);border-radius:14px;padding:12px 16px;box-shadow:var(--shadow);margin-top:20px}
.how summary{cursor:pointer;font-weight:800;color:var(--navy)}
.how ul{margin:8px 0 0;padding-left:1.2em;display:grid;gap:4px;max-width:65ch}
footer.site{margin-top:28px;display:flex;justify-content:space-between;gap:12px;flex-wrap:wrap;color:var(--muted);font-size:.85rem;font-weight:700}
footer.site a{color:var(--navy)}

@media (max-width:520px){
  .panel{padding-inline:14px}
  th,td{padding-inline:3px}
  thead th{white-space:normal;line-height:1.2;vertical-align:bottom}
  .tally .barcol{width:auto;min-width:84px}
  .tally td.match{width:5.6em}
  .tally td.num{width:2.2em;font-size:1.35rem}
  .match{white-space:normal;font-size:.82rem;line-height:1.2}
  .match .mark{margin-right:3px}
  .masstable{font-size:.9rem}
  .masstable .elcell span{display:none}
  .masstable tfoot th,.masstable tfoot td{font-size:.95rem}
}
@media (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important}}