/* Find My Mistake: Step Checker.
   Layout: Roji brand header, the student's work on the left like a sheet of notebook paper,
   Roji's verdict and help on the right (stacked on phones). The printed page is its own sheet
   and always prints as dark ink on white paper. */
: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;
  --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;
  --f-math:"Nunito","Cambria Math","Segoe UI Symbol",system-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;
  --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;
  --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,textarea{font-family:inherit}
:focus-visible{outline:3px solid var(--green);outline-offset:2px}
p{margin:0}

/* ---------- 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:.42em;letter-spacing:.03em;-webkit-text-stroke:0;text-shadow:none;color:var(--navy);vertical-align:.35em;white-space:nowrap}
.tagline{color:var(--muted);font-weight:700;max-width:56ch}
.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))}

.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}

/* ---------- layout ---------- */
.app{display:grid;grid-template-columns:minmax(0,1.35fr) 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}
.grp{padding-top:14px;display:grid;gap:10px}
.grp h2,.side 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)}
.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;font-size:1.05rem;padding-inline:22px}
.actions{display:flex;flex-wrap:wrap;gap:8px}

/* ---------- the work: one step per line, like notebook paper ---------- */
.lines{list-style:none;margin:0;padding:0;display:grid}
.line{display:grid;grid-template-columns:34px minmax(0,1fr) 40px;gap:0 8px;align-items:start;padding:10px 8px 10px 0;border-bottom:2px solid var(--line);border-left:5px solid transparent;border-radius:4px}
.line:first-child{border-top:2px solid var(--line)}
.line .num{font-family:var(--f-display);font-size:1.15rem;color:var(--muted);text-align:center;line-height:46px;font-variant-numeric:tabular-nums}
.entry{min-width:0;display:grid;gap:6px}
.entry input{font-family:var(--f-math);font-size:1.15rem;font-weight:700;color:var(--ink);background:var(--field);border:2px solid var(--line);border-radius:10px;padding:8px 12px;width:100%;min-width:0;min-height:46px}
.entry input:focus{border-color:var(--sky);outline:none;box-shadow:0 0 0 3px color-mix(in srgb,var(--sky) 25%,transparent)}
.entry input::placeholder{color:var(--muted);opacity:.7;font-weight:600}
.rm{width:40px;height:46px;border:0;background:transparent;color:var(--muted);border-radius:10px;font-size:1.3rem;font-weight:800;cursor:pointer}
.rm:hover{background:var(--tint)}
.reads{display:flex;flex-wrap:wrap;align-items:center;gap:4px 10px;min-height:0;color:var(--muted);font-size:.8rem;font-weight:800;overflow-x:auto}
.reads .lbl{text-transform:uppercase;letter-spacing:.07em;font-size:.68rem}
.reads:empty{display:none}
.fb{display:flex;flex-wrap:wrap;gap:6px 10px;align-items:baseline;font-weight:700;font-size:.95rem;max-width:62ch}
.fb:empty{display:none}
.tag{flex:none;font-size:.7rem;font-weight:800;text-transform:uppercase;letter-spacing:.06em;border-radius:999px;padding:3px 9px;background:var(--tint);color:var(--navy);white-space:nowrap}
.fb .say{flex:1 1 220px;min-width:0}

.line[data-status="ok"],.line[data-status="back"]{border-left-color:var(--green)}
.line[data-status="ok"] .tag,.line[data-status="back"] .tag{background:var(--ok-bg);color:var(--ok-ink)}
.line[data-status="ok"] .say,.line[data-status="start"] .say,.line[data-status="waiting"] .say{color:var(--muted)}
.line[data-status="wrong"]{border-left-color:var(--miss);background:var(--miss-bg)}
.line[data-status="wrong"] .tag{background:var(--miss);color:#fff}
.line[data-status="wrong"] .say{color:var(--miss-ink)}
.line[data-status="wrong"] .entry input{border-color:var(--miss)}
.line[data-status="carried"]{border-left-color:var(--line)}
.line[data-status="carried"] .say{color:var(--muted)}
.line[data-status="unreadable"]{border-left-color:var(--warn-ink);background:var(--warn-bg)}
.line[data-status="unreadable"] .tag{background:var(--warn-ink);color:var(--warn-bg)}
.line[data-status="unreadable"] .say{color:var(--warn-ink)}

/* math, drawn the way it looks in a textbook */
.m{font-family:var(--f-math);font-size:1.12rem;font-weight:700;color:var(--ink);display:inline-flex;align-items:center;flex-wrap:nowrap;white-space:nowrap;gap:.28em;line-height:1.15}
.m .g{display:inline-flex;align-items:center;gap:.28em}
.m .tight{display:inline-flex;align-items:center;gap:.06em}
.m .fr{display:inline-flex;flex-direction:column;align-items:center;font-size:.86em;line-height:1.1;vertical-align:middle}
.m .fr>span{padding:0 .3em;display:inline-flex;align-items:center;gap:.25em}
.m .fr>span:first-child{border-bottom:2px solid currentColor;padding-bottom:1px}
.m .fr>span:last-child{padding-top:1px}
.m sup{font-size:.68em;line-height:0;position:relative;top:-.55em;vertical-align:baseline}
.m i{font-style:italic;font-family:Georgia,"Times New Roman",serif;font-weight:700}
.m .rad{border-top:2px solid currentColor;padding:1px .2em 0 .1em;margin-left:-.1em}
.m .or{font-family:var(--f-body);font-size:.8em;color:var(--muted)}

/* math keys */
.keys{display:grid;grid-template-columns:repeat(8,minmax(0,1fr));gap:6px;position:sticky;bottom:env(safe-area-inset-bottom,0px);background:var(--surface);padding-block:8px;z-index:2}
.keys button{font-family:var(--f-math);font-size:1.1rem;font-weight:800;min-height:44px;border:2px solid var(--line);background:var(--tint);color:var(--ink);border-radius:10px;cursor:pointer;padding:0}
.keys button:active{background:var(--navy);color:var(--on-navy);border-color:var(--navy)}
.keys button small{font-size:.75em}
@media (max-width:520px){.line{grid-template-columns:26px minmax(0,1fr) 34px;gap:0 6px}.rm{width:34px}.panel{padding-inline:14px}}

/* ---------- Roji's verdict ---------- */
.side{min-width:0;display:grid;gap:14px}
.verdict{background:var(--navy);color:var(--on-navy);border-radius:18px;padding:16px 20px;display:grid;gap:8px;box-shadow:var(--shadow)}
.verdict .big{font-family:var(--f-display);font-size:clamp(1.6rem,5vw,2.1rem);line-height:1;padding-top:.12em;text-wrap:balance}
.verdict .small{font-weight:700;font-size:1rem;line-height:1.35}
.strip{display:flex;flex-wrap:wrap;gap:6px;align-items:center;margin-top:4px}
.dot{width:26px;height:26px;border-radius:50%;border:2px solid var(--on-navy);font-size:.75rem;font-weight:800;display:grid;place-items:center;font-variant-numeric:tabular-nums;flex:none}
.dot.ok,.dot.back{background:var(--green);border-color:var(--green);color:#06301B}
.dot.wrong{background:var(--miss);border-color:var(--on-navy);color:#fff;box-shadow:0 0 0 2px var(--navy),0 0 0 4px var(--on-navy)}
.dot.carried,.dot.waiting{opacity:.55}
.dot.unreadable{background:var(--warn-bg);border-color:var(--warn-bg);color:var(--warn-ink)}
.strip-key{font-size:.78rem;font-weight:700;opacity:.9}

.tools{display:grid;gap:8px}
.tools .hint:empty,.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)}
.how p{margin-top:8px;max-width:65ch}
.how ul{margin:8px 0 0;padding-left:1.2em;display:grid;gap:4px}
.how code{font-family:var(--f-math);font-weight:800;background:var(--tint);border-radius:6px;padding:1px 6px;white-space:nowrap}
.typing{display:grid;grid-template-columns:auto minmax(0,1fr);gap:6px 12px;margin:8px 0 0;align-items:baseline}
.typing dt{font-weight:700;color:var(--muted)}
.typing dd{margin:0}

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 work (US Letter). Fixed paper colors: this is what prints. ---------- */
.sheet{display:none}
@page{size:letter;margin:.5in}
@media print{
  body{background:#fff;color:#16324A}
  .wrap{display:none!important}
  .sheet{display:block;font-family:var(--f-body);color:#16324A;font-size:11pt;line-height:1.35}
  .sheet .m{color:#16324A;font-size:13pt}
  .sh-head{display:flex;justify-content:space-between;gap:16px;align-items:flex-end;border-bottom:2px solid #1D5B8D;padding-bottom:8px}
  .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:22pt;line-height:1;color:#1D5B8D;margin:2px 0 4px}
  .sh-meta{font-weight:700;color:#4F6A82;font-size:10pt}
  .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-table{width:100%;border-collapse:collapse;margin-top:8px}
  .sh-table th{font-size:8pt;text-transform:uppercase;letter-spacing:.08em;text-align:left;color:#4F6A82;padding:4px 6px;border-bottom:1.5px solid #C5D6E5}
  .sh-table td{padding:8px 6px;border-bottom:1px solid #C5D6E5;vertical-align:middle}
  .sh-table tr{break-inside:avoid}
  .sh-n{font-weight:800;color:#4F6A82;width:.4in}
  .sh-mark{font-weight:800;white-space:nowrap;width:1.2in}
  .sh-say{font-size:9.5pt;font-weight:600;color:#4F6A82;width:3in}
  .sh-wrong td{background:#FFE7E0}
  .sh-wrong .sh-say,.sh-wrong .sh-mark{color:#8F2A12}
  .sh-sum{margin-top:10px;font-weight:800;color:#1D5B8D}
  .sh-fix{margin-top:14px;font-size:9.5pt;font-weight:700;color:#4F6A82}
  .sh-fix i{display:block;border-bottom:1px solid #C5D6E5;height:.42in}
  .sh-foot{margin-top:12px;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}
}