/* CalculusSolver design system — vanilla CSS, no framework, system fonts only for zero font-load latency */

:root{
  --color-bg:#ffffff;
  --color-bg-alt:#f6f7fb;
  --color-surface:#ffffff;
  --color-border:#e3e6ef;
  --color-text:#1c2033;
  --color-text-muted:#5b6072;
  --color-primary:#4338ca;
  --color-primary-dark:#332a9e;
  --color-primary-light:#eef0fd;
  --color-accent:#0ea5a4;
  --color-success:#1a8f4c;
  --color-danger:#c0392b;
  --radius-sm:6px;
  --radius-md:10px;
  --radius-lg:16px;
  --shadow-sm:0 1px 2px rgba(20,20,43,.06);
  --shadow-md:0 6px 20px rgba(20,20,43,.08);
  --max-width:1120px;
  --font-sans:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,Helvetica,Arial,sans-serif;
  --font-mono:ui-monospace,SFMono-Regular,Menlo,Consolas,"Liberation Mono",monospace;
}

*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;text-size-adjust:100%}
body{
  margin:0;
  font-family:var(--font-sans);
  color:var(--color-text);
  background:var(--color-bg);
  line-height:1.6;
  font-size:17px;
}
img{max-width:100%;display:block}
a{color:var(--color-primary);text-decoration:none}
a:hover{text-decoration:underline}
h1,h2,h3,h4{line-height:1.25;font-weight:700;color:var(--color-text)}
h1{font-size:clamp(1.7rem,1.3rem + 1.6vw,2.4rem);margin:0 0 .5rem}
h2{font-size:clamp(1.3rem,1.1rem + 1vw,1.7rem);margin:2.2rem 0 .8rem}
h3{font-size:1.15rem;margin:1.6rem 0 .6rem}
p{margin:0 0 1rem}
ul,ol{padding-left:1.3rem}
li{margin-bottom:.4rem}
code,kbd{font-family:var(--font-mono);background:var(--color-bg-alt);padding:.15em .4em;border-radius:4px;font-size:.9em}

.container{max-width:var(--max-width);margin:0 auto;padding:0 20px}

/* Skip link for accessibility */
.skip-link{position:absolute;left:-999px;top:0;background:var(--color-primary);color:#fff;padding:.6em 1em;border-radius:0 0 8px 0;z-index:1000}
.skip-link:focus{left:0}

/* Header */
.site-header{border-bottom:1px solid var(--color-border);position:sticky;top:0;background:#fff;z-index:100}
.site-header .container{display:flex;align-items:center;justify-content:space-between;height:64px;gap:16px}
.brand{display:flex;align-items:center;gap:8px;font-weight:800;font-size:1.15rem;color:var(--color-text)}
.brand:hover{text-decoration:none}
.brand svg{flex:none}
.main-nav{display:flex;align-items:center;gap:22px}
.main-nav a{color:var(--color-text);font-weight:600;font-size:.95rem}
.main-nav a:hover{color:var(--color-primary);text-decoration:none}
.nav-toggle{display:none;background:none;border:1px solid var(--color-border);border-radius:8px;padding:8px 10px;cursor:pointer}

@media (max-width:760px){
  .nav-toggle{display:inline-flex}
  .main-nav{position:fixed;top:64px;left:0;right:0;bottom:0;background:#fff;flex-direction:column;align-items:flex-start;padding:20px;gap:4px;transform:translateX(100%);transition:transform .2s ease;overflow-y:auto;z-index:99}
  .main-nav.open{transform:translateX(0)}
  .main-nav a{width:100%;padding:12px 4px;border-bottom:1px solid var(--color-border)}
}

/* Breadcrumbs */
.breadcrumbs{font-size:.85rem;color:var(--color-text-muted);margin:16px 0}
.breadcrumbs a{color:var(--color-text-muted)}
.breadcrumbs li{display:inline}
.breadcrumbs ol{list-style:none;padding:0;margin:0}
.breadcrumbs li:not(:last-child)::after{content:"›";margin:0 8px;color:var(--color-border)}

/* Hero */
.hero{background:linear-gradient(180deg,var(--color-primary-light),#fff 70%);padding:56px 0 40px;border-bottom:1px solid var(--color-border)}
.hero h1{margin-bottom:.6rem}
.hero p.lead{font-size:1.1rem;color:var(--color-text-muted);max-width:640px}
.search-box{margin-top:22px;max-width:480px;position:relative}
.search-box input{width:100%;padding:13px 16px;font-size:1rem;border:1px solid var(--color-border);border-radius:var(--radius-md);box-shadow:var(--shadow-sm)}
.search-box input:focus{outline:2px solid var(--color-primary);outline-offset:1px}
.search-results{position:absolute;top:calc(100% + 6px);left:0;right:0;background:#fff;border:1px solid var(--color-border);border-radius:var(--radius-md);box-shadow:var(--shadow-md);max-height:320px;overflow-y:auto;display:none;z-index:50}
.search-results.show{display:block}
.search-results a{display:block;padding:10px 14px;color:var(--color-text);border-bottom:1px solid var(--color-border)}
.search-results a:hover{background:var(--color-bg-alt);text-decoration:none}
.search-results .sr-empty{padding:14px;color:var(--color-text-muted)}

/* Sections */
.section{padding:40px 0}
.section-head{display:flex;align-items:baseline;justify-content:space-between;gap:12px;flex-wrap:wrap}
.section-head h2{margin-top:0}

/* Cards / grid */
.grid{display:grid;gap:16px}
.grid-tools{grid-template-columns:repeat(auto-fill,minmax(250px,1fr))}
.grid-categories{grid-template-columns:repeat(auto-fill,minmax(220px,1fr))}

.card{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius-md);padding:18px;box-shadow:var(--shadow-sm);transition:transform .12s ease, box-shadow .12s ease}
a.card{display:block;color:var(--color-text)}
a.card:hover{transform:translateY(-2px);box-shadow:var(--shadow-md);text-decoration:none;border-color:var(--color-primary)}
.card .tag{display:inline-block;font-size:.72rem;font-weight:700;letter-spacing:.03em;text-transform:uppercase;color:var(--color-primary);background:var(--color-primary-light);padding:2px 8px;border-radius:999px;margin-bottom:8px}
.card h3{margin:0 0 6px;font-size:1.05rem}
.card p{margin:0;color:var(--color-text-muted);font-size:.92rem}

.planned-list{display:flex;flex-wrap:wrap;gap:8px;margin:10px 0 0}
.planned-list span{background:var(--color-bg-alt);border:1px dashed var(--color-border);color:var(--color-text-muted);font-size:.82rem;padding:4px 10px;border-radius:999px}

/* Tool page layout */
.tool-page .hero{padding:34px 0 26px}
.tool-layout{padding:8px 0 20px}

.calculator{background:var(--color-surface);border:1px solid var(--color-border);border-radius:var(--radius-lg);box-shadow:var(--shadow-md);padding:22px;margin:18px 0 30px}
.calculator h2{margin-top:0}
.calc-row{display:flex;gap:12px;flex-wrap:wrap;align-items:flex-end;margin-bottom:14px}
.calc-field{flex:1;min-width:160px}
.calc-field label{display:block;font-weight:600;font-size:.85rem;margin-bottom:5px;color:var(--color-text-muted)}
.calc-field input,.calc-field select{width:100%;padding:11px 12px;border:1px solid var(--color-border);border-radius:var(--radius-sm);font-size:1rem;font-family:var(--font-mono);background:#fff}
.calc-field input:focus,.calc-field select:focus{outline:2px solid var(--color-primary);outline-offset:1px}
.calc-actions{display:flex;gap:10px;flex-wrap:wrap}
.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;background:var(--color-primary);color:#fff;border:none;padding:12px 20px;border-radius:var(--radius-sm);font-weight:700;font-size:.95rem;cursor:pointer;transition:background .12s ease}
.btn:hover{background:var(--color-primary-dark)}
.btn.secondary{background:#fff;color:var(--color-primary);border:1px solid var(--color-primary)}
.btn.secondary:hover{background:var(--color-primary-light)}
.example-chips{display:flex;flex-wrap:wrap;gap:8px;margin:4px 0 16px}
.example-chips button{background:var(--color-bg-alt);border:1px solid var(--color-border);border-radius:999px;padding:5px 12px;font-size:.82rem;font-family:var(--font-mono);cursor:pointer;color:var(--color-text)}
.example-chips button:hover{background:var(--color-primary-light);border-color:var(--color-primary)}

.result-panel{margin-top:18px;border-top:1px solid var(--color-border);padding-top:16px;display:none}
.result-panel.show{display:block}
.result-main{background:var(--color-primary-light);border:1px solid #d9dcfb;border-radius:var(--radius-md);padding:16px;font-size:1.15rem;font-family:var(--font-mono);overflow-x:auto}
.steps{margin-top:14px}
.step{padding:10px 0;border-bottom:1px solid var(--color-border)}
.step:last-child{border-bottom:none}
.step .step-label{font-weight:700;font-size:.82rem;color:var(--color-primary);text-transform:uppercase;letter-spacing:.02em}
.step .step-expr{font-family:var(--font-mono);margin-top:2px;overflow-x:auto}
.error-msg{color:var(--color-danger);background:#fdecea;border:1px solid #f4c7c1;border-radius:var(--radius-sm);padding:10px 14px;font-size:.92rem;margin-top:10px}
.graph-wrap{margin-top:16px}
canvas.plot{width:100%;height:320px;border:1px solid var(--color-border);border-radius:var(--radius-md);background:#fff;touch-action:none}

/* Content */
.content-article{max-width:800px}
.content-article h2{border-top:1px solid var(--color-border);padding-top:24px}
.content-article h2:first-of-type{border-top:none;padding-top:0}
.faq details{border:1px solid var(--color-border);border-radius:var(--radius-sm);padding:12px 16px;margin-bottom:10px}
.faq summary{font-weight:700;cursor:pointer}
.faq p{margin-top:8px}
table.calc-table{width:100%;border-collapse:collapse;margin:1rem 0}
table.calc-table th,table.calc-table td{border:1px solid var(--color-border);padding:8px 10px;text-align:left;font-size:.92rem}
table.calc-table th{background:var(--color-bg-alt)}

.related-tools{margin-top:10px}

.callout{background:var(--color-bg-alt);border-left:4px solid var(--color-primary);border-radius:0 var(--radius-sm) var(--radius-sm) 0;padding:14px 16px;margin:1rem 0}

/* Footer */
.site-footer{background:#161826;color:#c7c9d9;margin-top:60px;padding:44px 0 26px}
.site-footer a{color:#c7c9d9}
.site-footer a:hover{color:#fff}
.footer-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(160px,1fr));gap:24px}
.footer-grid h4{color:#fff;font-size:.85rem;text-transform:uppercase;letter-spacing:.04em;margin:0 0 12px}
.footer-grid ul{list-style:none;padding:0;margin:0}
.footer-grid li{margin-bottom:8px;font-size:.9rem}
.footer-bottom{margin-top:32px;padding-top:20px;border-top:1px solid #2b2e42;font-size:.82rem;display:flex;justify-content:space-between;flex-wrap:wrap;gap:10px;color:#8b8ea3}

.badge-row{display:flex;gap:10px;flex-wrap:wrap;margin:10px 0 0}
.badge{font-size:.78rem;background:var(--color-bg-alt);border:1px solid var(--color-border);padding:4px 10px;border-radius:6px;color:var(--color-text-muted)}

.visually-hidden{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}