:root{
  --navy:#1c2434; --navy-mid:#2d3a52; --saffron:#ea580c; --saffron-d:#c2410c;
  --cream:#fbf8f1; --ink:#1c1917; --mid:#57534e; --border:#e7e2d8; --white:#fff;
  --ok:#16a34a; --bad:#e11d48;
}
*{box-sizing:border-box}
html{overflow-x:clip}
body{margin:0;font-family:'Inter',system-ui,sans-serif;color:var(--ink);background:var(--cream);line-height:1.6}

/* nav */
.gk-nav{display:flex;align-items:center;gap:24px;padding:14px clamp(16px,4vw,40px);background:var(--navy);color:#fff;position:sticky;top:0;z-index:10}
.gk-brand{font-family:'Fraunces',serif;font-weight:700;font-size:1.4rem;display:flex;align-items:center;gap:10px}
.gk-logo{display:inline-grid;place-items:center;width:34px;height:34px;background:var(--saffron);border-radius:9px;font-size:1.2rem}
.gk-by{font-family:'Inter';font-weight:500;font-size:.72rem;opacity:.7;letter-spacing:.02em}
.gk-tabs{margin-left:auto;display:flex;gap:6px}
.gk-tab{background:transparent;border:0;color:#cbd5e1;font-weight:600;font-size:.95rem;padding:8px 16px;border-radius:8px;cursor:pointer}
.gk-tab:hover{color:#fff;background:rgba(255,255,255,.08)}
.gk-tab.active{color:#fff;background:var(--saffron)}

/* layout */
.gk-main{max-width:980px;margin:0 auto;padding:clamp(24px,4vw,44px) clamp(16px,4vw,40px) 60px}
.gk-h1{font-family:'Fraunces',serif;font-size:clamp(1.7rem,4vw,2.4rem);color:var(--navy);margin:0 0 6px}
.gk-sub{color:var(--mid);margin:0 0 22px}

/* format guide */
.gk-guide{background:#fff;border:1px solid var(--border);border-radius:12px;padding:8px 16px;margin-bottom:18px}
.gk-guide summary{cursor:pointer;font-weight:700;color:var(--navy);padding:6px 0;font-size:.95rem}
.gk-guide__grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(230px,1fr));gap:10px 18px;padding:10px 0 6px}
.gk-guide__grid>div{display:flex;flex-direction:column;gap:2px;font-size:.85rem}
.gk-guide__grid b{color:var(--saffron-d);font-size:.74rem;text-transform:uppercase;letter-spacing:.03em}
.gk-guide__grid code{background:#f7f3ee;border:1px solid var(--border);border-radius:6px;padding:2px 7px;font-family:ui-monospace,monospace;font-size:.86rem;color:var(--ink);width:fit-content}
.gk-guide__grid span{color:var(--mid);font-size:.78rem}
.gk-guide kbd{background:#1c2434;color:#fff;border-radius:4px;padding:0 5px;font-size:.78rem}

/* processing spinner */
.gk-processing{display:flex;align-items:center;gap:12px;padding:18px 0;color:var(--mid)}
.gk-spin{width:22px;height:22px;border:3px solid #f0e6d8;border-top-color:var(--saffron);border-radius:50%;animation:gkspin .8s linear infinite;flex:none}
@keyframes gkspin{to{transform:rotate(360deg)}}
.gk-procstage{font-size:.92rem}

/* format error */
.gk-formaterr{background:#fff7ed;border:1.5px solid var(--saffron);border-left:5px solid var(--saffron);border-radius:12px;padding:16px 18px}
.gk-formaterr .t{font-weight:700;color:var(--saffron-d);margin-bottom:6px}
.gk-formaterr code{display:inline-block;background:#1c2434;color:#ffd9b0;border-radius:6px;padding:3px 9px;margin-top:6px;font-family:ui-monospace,monospace}

/* related formulas + similar questions */
.gk-related{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin-top:22px}
@media(max-width:680px){.gk-related{grid-template-columns:1fr}}
.gk-relbox{background:#fff;border:1px solid var(--border);border-radius:12px;padding:14px 16px}
.gk-relbox h4{margin:0 0 10px;font-size:.78rem;text-transform:uppercase;letter-spacing:.04em;color:var(--mid)}
.gk-relf{padding:7px 0;border-top:1px solid #f0ece4}
.gk-relf:first-of-type{border-top:0}
.gk-relf .nm{font-size:.86rem;font-weight:600;color:var(--navy)}
.gk-relf .fm{font-size:.95rem;margin-top:2px;overflow-x:auto}
.gk-relq{display:block;padding:7px 0;border-top:1px solid #f0ece4;color:var(--navy);text-decoration:none;font-size:.9rem}
.gk-relq:first-of-type{border-top:0}
.gk-relq:hover{color:var(--saffron-d)}
.gk-relq small{color:var(--mid)}
.gk-saved{font-size:.78rem;color:var(--ok);margin-top:10px}

/* solver */
.gk-solvebar{display:flex;gap:10px;flex-wrap:wrap}
#solveInput{flex:1;min-width:240px;font-size:1.05rem;padding:14px 16px;border:1.5px solid var(--border);border-radius:12px;background:#fff;font-family:'Inter'}
#solveInput:focus{outline:none;border-color:var(--saffron)}
.gk-btn{background:var(--saffron);color:#fff;border:0;font-weight:700;font-size:1rem;padding:0 26px;border-radius:12px;cursor:pointer;min-height:48px}
.gk-btn:hover{background:var(--saffron-d)}
.gk-btn--ghost{background:#fff;color:var(--navy);border:1.5px solid var(--border)}
.gk-examples{margin:16px 0 4px;color:var(--mid);font-size:.9rem;display:flex;gap:8px;flex-wrap:wrap;align-items:center}
.gk-ex{background:#fff;border:1px solid var(--border);border-radius:50px;padding:5px 13px;font-size:.84rem;color:var(--navy);cursor:pointer;font-family:'Inter'}
.gk-ex:hover{border-color:var(--saffron);color:var(--saffron-d)}

/* output */
.gk-out{margin-top:26px}
.gk-problem{font-size:.8rem;text-transform:uppercase;letter-spacing:.06em;color:var(--mid);font-weight:700;margin-bottom:4px}
.gk-answer{background:#fff;border:1.5px solid var(--ok);border-left:5px solid var(--ok);border-radius:12px;padding:16px 18px;margin-bottom:20px}
.gk-interpreted{font-size:.82rem;color:var(--mid);background:#fff7ed;border:1px solid #fed7aa;border-radius:8px;padding:6px 10px;margin-bottom:12px;font-family:ui-monospace,monospace}
.gk-explain{background:#eef6ff;border:1px solid #cfe3fb;border-left:4px solid #2563eb;border-radius:12px;padding:12px 15px;margin-bottom:18px}
.gk-explain-h{font-size:.72rem;font-weight:800;letter-spacing:.04em;text-transform:uppercase;color:#1d4ed8;margin-bottom:5px}
.gk-explain-b{font-size:.96rem;line-height:1.6;color:var(--ink)}
.gk-sug{background:#fff;border:1px solid var(--border);border-radius:12px;margin:8px 0 4px;overflow:hidden;box-shadow:0 6px 18px rgba(0,0,0,.07)}
.gk-sug-h{font-size:.68rem;font-weight:800;text-transform:uppercase;letter-spacing:.04em;color:var(--mid);padding:9px 14px 4px}
.gk-sug-q,.gk-sug-f{display:block;width:100%;text-align:left;background:none;border:0;border-top:1px solid #f0ece4;padding:9px 14px;font-size:.9rem;color:var(--navy);text-decoration:none;cursor:pointer;font-family:inherit}
.gk-sug-q:hover,.gk-sug-f:hover{background:#fff7ed;color:var(--saffron-d)}
.gk-sug-q small{color:var(--mid)}
.gk-sug-f .nm{font-weight:600}
.gk-sug-f .sub{color:var(--mid);font-size:.78rem;margin-left:8px}
.gk-answer .lbl{font-size:.72rem;font-weight:800;letter-spacing:.06em;text-transform:uppercase;color:var(--ok)}
.gk-answer .val{font-size:1.3rem;margin-top:4px}
.gk-mcq-answer .lbl::before{content:"\2713  "}
.gk-mcq-opts{display:flex;flex-direction:column;gap:7px;margin:-6px 0 20px}
.gk-mcq-opt{display:flex;align-items:center;gap:10px;padding:9px 13px;border:1px solid var(--border);border-radius:10px;background:#fff;font-size:1rem;color:var(--ink)}
.gk-mcq-opt .tag{font-weight:800;color:var(--mid);min-width:32px}
.gk-mcq-opt.is-correct{border-color:var(--ok);background:#f0fdf4}
.gk-mcq-opt.is-correct .tag{color:var(--ok)}
.gk-steps{display:flex;flex-direction:column;gap:0}
.gk-step{display:grid;grid-template-columns:34px 1fr;gap:14px;padding:16px 0;border-top:1px solid var(--border)}
.gk-step:first-child{border-top:0}
.gk-step .n{width:30px;height:30px;border-radius:50%;background:var(--navy);color:#fff;font-weight:700;font-size:.85rem;display:grid;place-items:center}
.gk-step .body .math{font-size:1.12rem;margin:2px 0 8px;overflow-x:auto}
.gk-step .body .exp{color:var(--mid);font-size:.95rem}
.gk-err{background:#fff;border:1.5px solid var(--bad);border-left:5px solid var(--bad);border-radius:12px;padding:16px 18px;color:var(--bad)}
.gk-engine{font-size:.74rem;color:var(--mid);margin-top:14px;opacity:.8}

/* library */
.gk-libbar{display:flex;gap:10px;flex-wrap:wrap;margin-bottom:20px}
#libSearch{flex:1;min-width:220px;font-size:1rem;padding:12px 14px;border:1.5px solid var(--border);border-radius:10px;background:#fff}
#libSubject,#libGrade{font-size:.95rem;padding:12px 12px;border:1.5px solid var(--border);border-radius:10px;background:#fff}
#libSearch:focus,#libSubject:focus,#libGrade:focus{outline:none;border-color:var(--saffron)}
.gk-cards{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:14px}
.gk-card{background:#fff;border:1px solid var(--border);border-radius:14px;padding:15px 16px;border-left:4px solid var(--saffron)}
.gk-card .top{display:flex;justify-content:space-between;gap:8px;align-items:center;margin-bottom:6px}
.gk-card .subj{font-size:.66rem;font-weight:800;text-transform:uppercase;letter-spacing:.04em;color:var(--saffron-d);background:#fff4ed;padding:3px 9px;border-radius:50px}
.gk-card .gr{font-size:.7rem;color:var(--mid)}
.gk-card h3{margin:0 0 8px;font-size:1.02rem;color:var(--navy)}
.gk-card .fml{font-size:1.05rem;margin:6px 0;overflow-x:auto}
.gk-card .desc{font-size:.88rem;color:var(--mid)}
.gk-more{text-align:center;margin-top:20px}
.gk-foot{text-align:center;color:var(--mid);font-size:.84rem;padding:26px 20px;border-top:1px solid var(--border)}
@media(max-width:540px){.gk-tabs .gk-tab{padding:8px 10px;font-size:.88rem}}