/* Sig Figs & Scientific Notation Helper.
   Layout: Roji brand header, four big tabs (count, round, scientific notation, calculate), the student's
   number on the left, and on the right a navy card that shows each digit as a tile and names the rule
   that applied (stacked on phones). */
: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;
  --miss:#E2573B; --miss-bg:#FFE7E0; --miss-ink:#8F2A12;
  --card:#1D5B8D; --card-ink:#FFFFFF; --card-soft:#CFE3F3; --card-line:rgba(255,255,255,.22);
  --tile:#FFFFFF; --tile-ink:#16324A; --tile-off:rgba(255,255,255,.10); --tile-off-ink:#CFE3F3;
  --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;
  --miss:#FF8A70; --miss-bg:#43201A; --miss-ink:#FFC2B3;
  --card:#1A3A57; --card-ink:#E6F0F8; --card-soft:#A9C4DA; --card-line:rgba(255,255,255,.16);
  --tile:#E6F0F8; --tile-ink:#0E1B27; --tile-off:rgba(255,255,255,.07); --tile-off-ink:#A9C4DA;
  --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;
  --miss:#FF8A70; --miss-bg:#43201A; --miss-ink:#FFC2B3;
  --card:#1A3A57; --card-ink:#E6F0F8; --card-soft:#A9C4DA; --card-line:rgba(255,255,255,.16);
  --tile:#E6F0F8; --tile-ink:#0E1B27; --tile-off:rgba(255,255,255,.07); --tile-off-ink:#A9C4DA;
  --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}
html{padding-top:env(safe-area-inset-top,0px);padding-bottom:env(safe-area-inset-bottom,0px)}
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,textarea{font-family:inherit}
:focus-visible{outline:3px solid var(--green);outline-offset:2px}
p{margin:0}
.nowrapnum{white-space:nowrap}
sup{font-size:.62em;line-height:0;vertical-align:.62em;font-weight:inherit}

/* ---------- 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(1.9rem,5.2vw,3.3rem);line-height:.98;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:.46em;letter-spacing:.03em;-webkit-text-stroke:0;text-shadow:none;color:var(--navy);vertical-align:.3em;white-space:nowrap}
.tagline{color:var(--muted);font-weight:700;max-width:58ch}
.roji{flex:0 0 auto;width:clamp(104px,19vw,190px);display:block}
.roji img{width:100%;height:auto;display:block;filter:drop-shadow(0 8px 12px rgba(18,52,79,.18))}

.example{display:flex;flex-wrap:wrap;gap:8px 14px;align-items:center;justify-content:space-between;background:var(--warn-bg);color:var(--warn-ink);
  border-radius:14px;padding:10px 14px;font-weight:700;margin-bottom:16px}
.example .btn.ghost{color:var(--warn-ink);border-color:currentColor}

/* ---------- the four jobs ---------- */
.modes{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:8px;margin-bottom:16px}
.modes button{display:grid;gap:1px;text-align:left;border:2px solid var(--line);background:var(--surface);color:var(--ink);border-radius:14px;padding:10px 14px;min-height:60px;cursor:pointer;min-width:0}
.modes b{font-family:var(--f-display);font-weight:400;font-size:1.15rem;line-height:1.1;letter-spacing:.02em;color:var(--navy);padding-top:.1em}
.modes span{font-size:.8rem;font-weight:700;color:var(--muted);line-height:1.25}
.modes button[aria-pressed="true"]{background:var(--navy);border-color:var(--navy)}
.modes button[aria-pressed="true"] b{color:var(--on-navy)}
.modes button[aria-pressed="true"] span{color:var(--on-navy);opacity:.85}
@media (max-width:760px){.modes{grid-template-columns:repeat(2,minmax(0,1fr))}}

/* ---------- layout ---------- */
.app{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.25fr);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}
@media (max-width:520px){.panel{padding-inline:14px}}
.grp{padding-top:14px;display:grid;gap:10px}
.grp h2,.tools h2{font-size:.78rem;text-transform:uppercase;letter-spacing:.08em;color:var(--green-ink);margin:0;font-weight:800}
.hint{font-weight:600;font-size:.85rem;color:var(--muted)}
.hint:empty{display:none}
.err{font-weight:700;font-size:.9rem;color:var(--miss-ink);background:var(--miss-bg);border-radius:10px;padding:7px 11px}
.err:empty{display:none}
.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)}
.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.go{background:var(--green);border-color:var(--green);color:#06301B}
.btn:disabled{opacity:.45;cursor:not-allowed}
.actions{display:flex;flex-wrap:wrap;gap:8px;align-items:center}

.field{display:grid;gap:4px;min-width:0}
.field>span{font-size:.82rem;font-weight:800;color:var(--muted)}
input.num{font-size:1.25rem;font-weight:800;letter-spacing:.02em;font-variant-numeric:tabular-nums;color:var(--ink);background:var(--field);border:2px solid var(--line);border-radius:10px;padding:8px 12px;width:100%;min-width:0;min-height:50px}
input.num:focus{border-color:var(--sky);outline:none;box-shadow:0 0 0 3px color-mix(in srgb,var(--sky) 25%,transparent)}
input.num::placeholder{color:var(--muted);opacity:.6;font-weight:600}
input.num.bad{border-color:var(--miss);background:var(--miss-bg);color:var(--miss-ink)}
.stepper{display:flex;align-items:center;gap:10px}
.stepper button{width:44px;height:44px;border-radius:12px;border:2px solid var(--navy);background:transparent;color:var(--navy);font-size:1.4rem;font-weight:800;cursor:pointer;line-height:1}
.stepper output{font-family:var(--f-display);font-size:1.8rem;min-width:1.6ch;text-align:center;color:var(--navy);padding-top:.12em;font-variant-numeric:tabular-nums}

/* calculate rows */
.rows{display:grid;gap:8px}
.row{display:grid;grid-template-columns:54px minmax(0,1fr) auto;gap:8px;align-items:center}
.row select{height:50px;border-radius:10px;border:2px solid var(--line);background:var(--field);color:var(--ink);font-size:1.3rem;font-weight:800;text-align:center;text-align-last:center;padding:0 4px;width:100%}
.row .first{font-size:.72rem;font-weight:800;color:var(--muted);text-transform:uppercase;letter-spacing:.06em;text-align:center}
.row .exact{display:flex;align-items:center;gap:6px;font-size:.82rem;font-weight:800;color:var(--muted);min-height:44px;cursor:pointer;white-space:nowrap}
.row .exact input{width:20px;height:20px;accent-color:var(--navy)}
.row .rm{width:36px;height:44px;border:0;background:transparent;color:var(--muted);border-radius:10px;font-size:1.3rem;font-weight:800;cursor:pointer;padding:0}
.row .tail{display:flex;align-items:center;gap:2px}
.carried{display:flex;flex-wrap:wrap;align-items:center;gap:4px 10px;background:var(--tint);border-radius:10px;padding:8px 12px;min-height:50px;font-weight:800;font-variant-numeric:tabular-nums;min-width:0;overflow-wrap:anywhere}
.carried small{font-weight:700;color:var(--muted);font-size:.8rem}
.opt{display:flex;align-items:flex-start;gap:10px;min-height:44px;font-weight:700;cursor:pointer;padding-block:9px}
.opt input{width:22px;height:22px;accent-color:var(--navy);flex:none;margin:1px 0 0}

/* ---------- the answer card ---------- */
.side{min-width:0;display:grid;gap:14px}
.verdict{background:var(--card);color:var(--card-ink);border-radius:18px;padding:16px 20px;display:grid;gap:10px;box-shadow:var(--shadow);min-width:0}
@media (max-width:520px){.verdict{padding-inline:14px}}
.vhead{font-size:.78rem;text-transform:uppercase;letter-spacing:.08em;font-weight:800;color:var(--card-soft)}
.verdict .big{font-family:var(--f-display);font-size:clamp(1.7rem,5.5vw,2.5rem);line-height:1.05;padding-top:.12em;text-wrap:balance;overflow-wrap:anywhere;font-variant-numeric:tabular-nums}
.verdict .big small{font-family:var(--f-body);font-size:.42em;font-weight:800;color:var(--card-soft);display:block;line-height:1.3;padding-top:4px}
.sub{font-weight:700;color:var(--card-soft);font-size:.95rem}
.sub b{color:var(--card-ink)}
.cardnote{background:var(--warn-bg);color:var(--warn-ink);border-radius:10px;padding:8px 12px;font-weight:700;font-size:.92rem}

/* digit tiles: solid = counts, dashed = doesn't count, "?" = unclear */
.tilebox{overflow-x:auto;padding-bottom:4px;min-width:0}
.tiles{display:inline-flex;align-items:flex-start;gap:4px;font-variant-numeric:tabular-nums}
.tile{display:grid;justify-items:center;gap:3px;border:0;background:none;padding:0;color:inherit;cursor:pointer;font:inherit}
.tile .d{width:38px;height:48px;display:grid;place-items:center;border-radius:9px;font-size:1.6rem;font-weight:800;border:2px solid transparent;line-height:1}
.tile .m{font-size:.78rem;font-weight:800;height:1.1em;line-height:1.1;color:var(--card-soft)}
.tile.sig .d{background:var(--tile);color:var(--tile-ink);border-color:var(--tile)}
.tile.sig .m{color:var(--green)}
.tile.not .d{background:var(--tile-off);color:var(--tile-off-ink);border:2px dashed var(--card-soft)}
.tile.unclear .d{background:var(--warn-bg);color:var(--warn-ink);border:2px dashed var(--warn-ink)}
.tile.last .d{box-shadow:0 0 0 3px var(--green)}
.tile.decider .d{background:var(--warn-bg);color:var(--warn-ink);border-color:var(--warn-bg)}
.tile.drop .d{background:transparent;color:var(--card-soft);border:2px dashed var(--card-line);text-decoration:line-through}
.tile[aria-pressed="true"] .d{outline:3px solid var(--green);outline-offset:2px}
.tsep{font-size:1.6rem;font-weight:800;height:48px;display:grid;align-items:end;padding:0 1px 4px}
.tsep.times{align-items:center;padding:0 6px;font-size:1.25rem;white-space:nowrap}
@media (max-width:520px){.tile .d{width:30px;height:42px;font-size:1.3rem}.tsep{height:42px;font-size:1.3rem}.tsep.times{font-size:1.05rem}}
.why{font-weight:700;font-size:.95rem;min-height:1.5em;color:var(--card-soft)}
.why b{color:var(--card-ink)}

.checks{list-style:none;margin:0;padding:0;display:grid}
.checks li{display:grid;grid-template-columns:28px minmax(0,1fr);gap:10px;align-items:start;padding:8px 0;border-top:1px solid var(--card-line);font-weight:700;font-size:.95rem;line-height:1.35}
.checks li small{display:block;font-weight:600;color:var(--card-soft);font-size:.85rem}
.mark{width:26px;height:26px;border-radius:50%;border:2px solid var(--card-ink);display:grid;place-items:center;font-size:.82rem;font-weight:800;line-height:1;flex:none}
li[data-state="ok"] .mark{background:var(--green);border-color:var(--green);color:#06301B}
li[data-state="tip"] .mark{background:var(--warn-bg);border-color:var(--warn-bg);color:var(--warn-ink)}
li[data-state="no"] .mark{border-style:dashed}
.limit{display:inline-block;background:var(--warn-bg);color:var(--warn-ink);border-radius:999px;padding:0 9px;font-size:.78rem;font-weight:800;margin-left:6px;white-space:nowrap}

/* adding and subtracting: numbers lined up on the decimal point, with a cut line */
.colbox{overflow-x:auto;min-width:0}
.cols{display:inline-grid;gap:0;font-size:1.35rem;font-weight:800;font-variant-numeric:tabular-nums;line-height:1.45;background:var(--tile);color:var(--tile-ink);border-radius:10px;padding:8px 14px}
.cols span{text-align:center;min-width:.62em}
.cols .op{min-width:1.3em;text-align:left}
.cols .cut{border-right:3px dashed var(--miss);padding-right:3px;margin-right:3px}
.cols .gone{opacity:.38}
.cols .rule{grid-column:1/-1;border-top:3px solid currentColor;height:0;margin-block:3px}

/* try it first */
.try{display:grid;gap:10px}
.tryrow{display:flex;flex-wrap:wrap;gap:8px}
.tryrow input{flex:1 1 150px;min-width:0;font-size:1.2rem;font-weight:800;border-radius:10px;border:2px solid var(--tile);background:var(--tile);color:var(--tile-ink);padding:8px 12px;min-height:48px}
.verdict .btn.go{font-size:1rem}
.verdict .btn.ghost{color:var(--card-ink);border-color:var(--card-ink)}
.feedback{font-weight:800}
.feedback:empty{display:none}

.tools{display:grid;gap:10px}
.toast:empty{display:none}
.toast{background:var(--ok-bg);color:var(--ok-ink);border-radius:10px;padding:8px 12px;font-weight:700;font-size:.9rem}
.copybox{min-height:70px;font-size:.8rem;font-weight:600;word-break:break-all;color:var(--ink);background:var(--field);border:2px solid var(--line);border-radius:10px;padding:9px 10px;width:100%}
.how{background:var(--surface);border-radius:14px;padding:12px 16px;box-shadow:var(--shadow)}
.how summary{cursor:pointer;font-weight:800;color:var(--navy);min-height:28px}
.how p{margin-top:8px;max-width:65ch}
.how ul,.how ol{margin:8px 0 0;padding-left:1.3em;display:grid;gap:6px;max-width:65ch}
.how code{font-family:inherit;font-weight:800;background:var(--tint);border-radius:6px;padding:0 5px;font-variant-numeric:tabular-nums;white-space:nowrap}

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 (prefers-reduced-motion:reduce){*{transition:none!important;animation:none!important;scroll-behavior:auto!important}}

/* ---------- printed page (US Letter). Fixed paper colors: this is what prints. ---------- */
.sheet{display:none}
@page{size:letter;margin:.6in}
@media print{
  html{padding:0}
  body{background:#fff;color:#16324A}
  .wrap{display:none!important}
  .sheet{display:block;font-family:var(--f-body);color:#16324A;font-size:11pt;line-height:1.4}
  .sh-head{display:flex;justify-content:space-between;gap:16px;align-items:flex-end;border-bottom:2px solid #1D5B8D;padding-bottom:6px}
  .sh-eyebrow{font-size:8.5pt;text-transform:uppercase;letter-spacing:.09em;font-weight:800;color:#4F6A82}
  .sh-title{font-family:var(--f-display);font-weight:400;font-size:19pt;line-height:1;color:#1D5B8D;margin:2px 0 0}
  .sh-name{font-weight:700;white-space:nowrap;font-size:10pt}
  .sh-name i{display:inline-block;width:1.9in;border-bottom:1.5px solid #16324A}
  .sh-h{font-size:8.5pt;text-transform:uppercase;letter-spacing:.08em;font-weight:800;color:#4F6A82;margin:14px 0 4px}
  .sh-problem{font-size:17pt;font-weight:800;font-variant-numeric:tabular-nums}
  .sh-list{margin:0;padding-left:1.3em}
  .sh-list li{padding:2px 0;font-weight:600;break-inside:avoid}
  .sh-answer{font-size:15pt;font-weight:800;border:2px solid #1D5B8D;border-radius:8px;padding:6px 12px;display:inline-block;margin-top:6px;font-variant-numeric:tabular-nums}
  .sh-blank{display:inline-block;width:2.6in;border-bottom:1.5px solid #16324A;height:20pt}
  .sh-rules{margin:0;padding:0;list-style:none;columns:2;column-gap:.35in;font-size:9.5pt}
  .sh-rules li{break-inside:avoid;padding:2px 0;font-weight:600}
  .sh-foot{margin-top:16px;display:flex;align-items:center;gap:8px;font-weight:800;color:#1D5B8D;font-size:9pt;border-top:1px solid #C5D6E5;padding-top:6px}
  .sh-foot img{width:22pt;height:22pt;border-radius:50%}
  *{-webkit-print-color-adjust:exact;print-color-adjust:exact}
}
.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}