/* ===================== TOKENS ===================== */
:root{
  --bg: #0a0e18;
  --bg-elev: #101624;
  --bg-elev-2: #151d30;
  --border: #202a41;
  --text: #e9edf7;
  --text-dim: #9aa5c0;
  --text-faint: #6b7591;
  --accent: #5b8cff;
  --accent-2: #22d3c9;
  --accent-3: #ffb454;
  --accent-rgb: 91,140,255;
  --danger: #ff6b6b;
  --success: #34d399;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 20px;
  --shadow: 0 20px 50px -20px rgba(0,0,0,.55);
  --font-display: 'Outfit', sans-serif;
  --font-body: 'Inter', sans-serif;
  --header-h: 68px;
}

[data-theme="light"]{
  --bg: #f5f7fc;
  --bg-elev: #ffffff;
  --bg-elev-2: #eef1f9;
  --border: #dde3f0;
  --text: #131a2b;
  --text-dim: #4d5975;
  --text-faint: #7c869e;
  --shadow: 0 20px 50px -25px rgba(20,30,60,.25);
}

*, *::before, *::after{ box-sizing: border-box; }
html{ scroll-behavior: smooth; }
body{
  margin:0;
  background: var(--bg);
  color: var(--text);
  font-family: var(--font-body);
  font-size: 16px;
  line-height: 1.6;
  overflow-x: hidden;
  transition: background .25s ease, color .25s ease;
}
h1,h2,h3,h4{ font-family: var(--font-display); font-weight: 700; line-height: 1.2; margin: 0 0 .5em; color: var(--text); }
p{ margin: 0 0 1em; color: var(--text-dim); }
a{ color: inherit; text-decoration: none; }
img{ max-width: 100%; display:block; }
code{ font-family: 'SFMono-Regular', Consolas, monospace; }
ul,ol{ margin:0; padding:0; }
button{ font-family: inherit; }

.skip-link{
  position:absolute; left:-999px; top:0; background:var(--accent); color:#fff;
  padding:10px 16px; border-radius: 0 0 8px 0; z-index: 999;
}
.skip-link:focus{ left:0; }

:focus-visible{ outline: 2px solid var(--accent); outline-offset: 2px; }

.section-lead{ max-width: 680px; color: var(--text-dim); }

/* ===================== BUTTONS ===================== */
.btn{
  display:inline-flex; align-items:center; justify-content:center; gap:8px;
  padding: 12px 22px; border-radius: 999px; border: 1px solid transparent;
  font-weight: 600; font-size: .95rem; cursor:pointer; transition: transform .15s ease, background .2s ease, border-color .2s ease, opacity .2s;
  white-space: nowrap;
}
.btn:active{ transform: scale(.97); }
.btn-primary{ background: linear-gradient(135deg, var(--accent), var(--accent-2)); color:#06101f; }
.btn-primary:hover{ filter: brightness(1.08); }
.btn-primary:disabled{ opacity:.6; cursor:not-allowed; transform:none; }
.btn-outline{ border-color: var(--border); background: transparent; color: var(--text); }
.btn-outline:hover{ border-color: var(--accent); }
.btn-ghost{ background: transparent; color: var(--text-dim); border: 1px solid var(--border); }
.btn-ghost:hover{ color: var(--text); border-color: var(--accent); }
.btn-lg{ padding: 15px 30px; font-size: 1.02rem; }
.btn-small{ padding: 8px 16px; font-size: .85rem; }

.btn-spinner{
  width:14px; height:14px; border-radius:50%;
  border: 2px solid rgba(6,16,31,.35); border-top-color: #06101f;
  display:none; animation: spin .7s linear infinite;
}
.btn.is-loading .btn-spinner{ display:inline-block; }
.btn.is-loading .btn-label{ opacity:.7; }
@keyframes spin{ to{ transform: rotate(360deg); } }

/* ===================== HEADER ===================== */
.site-header{
  position: sticky; top:0; z-index: 100;
  background: rgba(10,14,24,.85); backdrop-filter: blur(14px);
  border-bottom: 1px solid var(--border);
  height: var(--header-h);
}
[data-theme="light"] .site-header{ background: rgba(245,247,252,.85); }
.header-inner{
  max-width: 1280px; margin:0 auto; height:100%;
  display:flex; align-items:center; justify-content:space-between;
  padding: 0 24px; gap: 20px;
}
.brand{ display:flex; align-items:center; gap:8px; flex-shrink:0; }
.brand-mark{ color: var(--accent); display:flex; }
.brand-text{ font-family: var(--font-display); font-weight:700; font-size:1.15rem; color:var(--text); }
.brand-dot{ color: var(--accent-2); }

.main-nav{ display:flex; align-items:center; gap: 4px; flex:1; justify-content:center; }
.nav-link{
  background:none; border:none; color: var(--text-dim); font-size:.95rem; font-weight:500;
  padding: 10px 14px; border-radius: 8px; cursor:pointer; display:flex; align-items:center; gap:5px;
  transition: color .2s, background .2s;
}
.nav-link:hover{ color: var(--text); background: var(--bg-elev-2); }
.chev{ transition: transform .2s; }
.nav-item.has-dropdown{ position: relative; }
.nav-item.has-dropdown.open .chev{ transform: rotate(180deg); }

.dropdown-panel{
  position:absolute; top: 100%; left: 50%; transform: translateX(-50%);
  width: 620px; max-width: 84vw;
  background: var(--bg-elev); border:1px solid var(--border); border-radius: var(--radius-md);
  box-shadow: var(--shadow);
  padding: 10px; margin-top: 8px;
  display:grid; grid-template-columns: repeat(2, 1fr); gap: 2px;
  opacity:0; visibility:hidden; transform: translateX(-50%) translateY(6px);
  transition: opacity .18s ease, transform .18s ease, visibility .18s;
}
.nav-item.has-dropdown.open .dropdown-panel{
  opacity:1; visibility:visible; transform: translateX(-50%) translateY(0);
}
.dropdown-panel a{
  padding: 9px 12px; border-radius: 8px; font-size: .88rem; color: var(--text-dim);
}
.dropdown-panel a:hover{ background: var(--bg-elev-2); color: var(--text); }

.header-actions{ display:flex; align-items:center; gap:10px; flex-shrink:0; }
.theme-toggle{
  width:38px; height:38px; border-radius:50%; border:1px solid var(--border);
  background: var(--bg-elev-2); color: var(--text-dim); display:flex; align-items:center; justify-content:center;
  cursor:pointer;
}
.theme-toggle:hover{ color: var(--accent); }
.icon-moon{ display:none; }
[data-theme="light"] .icon-sun{ display:none; }
[data-theme="light"] .icon-moon{ display:block; }

.nav-toggle{
  display:none; flex-direction:column; justify-content:center; gap:5px;
  width:38px; height:38px; border-radius:8px; border:1px solid var(--border);
  background: var(--bg-elev-2); cursor:pointer;
}
.nav-toggle span{ display:block; height:2px; width:18px; margin:0 auto; background: var(--text); border-radius:2px; transition: transform .2s, opacity .2s; }
.nav-toggle[aria-expanded="true"] span:nth-child(1){ transform: translateY(7px) rotate(45deg); }
.nav-toggle[aria-expanded="true"] span:nth-child(2){ opacity:0; }
.nav-toggle[aria-expanded="true"] span:nth-child(3){ transform: translateY(-7px) rotate(-45deg); }

/* ===================== BREADCRUMB ===================== */
.breadcrumb-wrap{ border-bottom: 1px solid var(--border); background: var(--bg-elev); }
.breadcrumb{ max-width: 1280px; margin: 0 auto; padding: 12px 24px; overflow-x:auto; }
.breadcrumb ol{ display:flex; align-items:center; gap:8px; list-style:none; white-space:nowrap; }
.breadcrumb li{ font-size:.85rem; color: var(--text-faint); }
.breadcrumb li:not(:last-child)::after{ content:'/'; margin-left:8px; color: var(--text-faint); }
.breadcrumb a{ color: var(--text-dim); }
.breadcrumb a:hover{ color: var(--accent); }
.breadcrumb li[aria-current]{ color: var(--text); font-weight:500; }

/* ===================== HERO ===================== */
.hero{ padding: 64px 24px 40px; position:relative; overflow:hidden; }
.hero::before{
  content:''; position:absolute; inset: -20% -10% auto -10%; height: 480px;
  background: radial-gradient(600px 300px at 20% 20%, rgba(var(--accent-rgb),.18), transparent 70%);
  pointer-events:none;
}
.hero-inner{
  max-width: 1280px; margin:0 auto; display:grid; grid-template-columns: 1.1fr .9fr;
  gap: 48px; align-items:center; position:relative;
}
.eyebrow{
  display:inline-block; font-size:.78rem; font-weight:600; letter-spacing:.04em; text-transform:uppercase;
  color: var(--accent-2); background: rgba(34,211,201,.1); border:1px solid rgba(34,211,201,.25);
  padding: 6px 12px; border-radius: 999px; margin-bottom: 18px;
}
.hero h1{ font-size: clamp(2.2rem, 5vw, 3.4rem); margin-bottom:.4em; }
.hero-sub{ font-size: 1.08rem; max-width: 540px; }
.hero-cta{ display:flex; gap:12px; flex-wrap:wrap; margin: 22px 0 16px; }
.hero-trust{ font-size:.85rem; color: var(--text-faint); }

.hero-visual{ display:flex; justify-content:center; }
.curve-svg{ width: 100%; max-width: 420px; }
.curve-path{ stroke-dasharray: 900; stroke-dashoffset: 900; animation: draw 1.8s ease forwards .2s; }
.tangent-line, .tangent-dot{ opacity:0; animation: fadeIn .6s ease forwards 1.7s; }
@keyframes draw{ to{ stroke-dashoffset: 0; } }
@keyframes fadeIn{ to{ opacity:1; } }
@media (prefers-reduced-motion: reduce){
  .curve-path{ animation:none; stroke-dashoffset:0; }
  .tangent-line, .tangent-dot{ animation:none; opacity:1; }
}

/* ===================== SHARE STRIP ===================== */
.share-strip{ border-top:1px solid var(--border); border-bottom:1px solid var(--border); background: var(--bg-elev); }
.share-inner{ max-width:1280px; margin:0 auto; padding: 14px 24px; display:flex; align-items:center; justify-content:center; gap:16px; flex-wrap:wrap; }
.share-label{ font-size:.85rem; color: var(--text-faint); font-weight:600; }
.share-links{ display:flex; gap:8px; }
.share-btn{
  width:34px; height:34px; border-radius:50%; display:flex; align-items:center; justify-content:center;
  background: var(--bg-elev-2); border:1px solid var(--border); color: var(--text-dim); cursor:pointer; transition: all .2s;
}
.share-btn:hover{ color:#fff; background: var(--accent); border-color: var(--accent); }

/* ===================== SOLVER ===================== */
.solver-section{ padding: 60px 24px; }
.solver-inner{ max-width: 900px; margin:0 auto; }
.solver-inner h2{ font-size: 1.8rem; }

.solver-form{
  margin-top: 24px; background: var(--bg-elev); border:1px solid var(--border);
  border-radius: var(--radius-lg); padding: 26px; box-shadow: var(--shadow);
}
.field-row{ display:grid; grid-template-columns: 2fr 1fr 1fr; gap: 16px; }
.input-group label{ display:block; font-size:.82rem; font-weight:600; color: var(--text-dim); margin-bottom:8px; }
.input-wrap{
  display:flex; align-items:center; background: var(--bg-elev-2); border: 1px solid var(--border);
  border-radius: var(--radius-sm); overflow:hidden; transition: border-color .2s, box-shadow .2s;
}
.input-wrap:focus-within{ border-color: var(--accent); box-shadow: 0 0 0 3px rgba(var(--accent-rgb),.18); }
.input-prefix{ padding: 0 0 0 14px; color: var(--text-faint); font-family: monospace; font-size:.95rem; }
#functionInput{
  flex:1; border:none; background:transparent; color: var(--text); padding: 13px 10px;
  font-size: 1rem; font-family: monospace; outline:none; min-width:0;
}
.clear-input{
  border:none; background:none; color: var(--text-faint); font-size:1.3rem; padding:0 14px; cursor:pointer; line-height:1;
}
.clear-input:hover{ color: var(--danger); }
.field-hint{ font-size:.78rem; color: var(--text-faint); margin: 8px 0 0; }
.field-error{ font-size:.8rem; color: var(--danger); margin: 6px 0 0; min-height: 1em; }

select{
  width:100%; padding: 13px 12px; border-radius: var(--radius-sm); border: 1px solid var(--border);
  background: var(--bg-elev-2); color: var(--text); font-size: .95rem; cursor:pointer;
}
select:focus{ border-color: var(--accent); }

.quick-examples{ display:flex; align-items:center; flex-wrap:wrap; gap:8px; margin-top: 18px; }
.quick-examples span{ font-size:.82rem; color: var(--text-faint); margin-right:4px; }
.chip{
  border: 1px solid var(--border); background: var(--bg-elev-2); color: var(--text-dim);
  padding: 6px 13px; border-radius: 999px; font-size:.82rem; font-family: monospace; cursor:pointer; transition: all .18s;
}
.chip:hover{ border-color: var(--accent); color: var(--text); }

.form-actions{ display:flex; gap:12px; margin-top: 22px; }
.field-row .input-group.has-error .input-wrap{ border-color: var(--danger); }

/* ===================== RESULTS ===================== */
.results-section{ padding: 10px 24px 60px; }
.results-inner{ max-width: 900px; margin: 0 auto; }
.results-header{ display:flex; align-items:center; justify-content:space-between; flex-wrap:wrap; gap:12px; margin-bottom:16px; }
.results-actions{ display:flex; gap:8px; }

.result-card{
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius-lg);
  padding: 22px 24px; box-shadow: var(--shadow); margin-bottom: 20px;
}
.result-row{ padding: 12px 0; border-bottom: 1px solid var(--border); display:flex; flex-direction:column; gap:6px; }
.result-row:last-child{ border-bottom:none; }
.result-label{ font-size:.78rem; text-transform:uppercase; letter-spacing:.04em; color: var(--text-faint); font-weight:600; }
.result-value{ font-family: monospace; font-size: 1.05rem; color: var(--text); word-break: break-word; }
.result-value-main{ font-size: 1.35rem; color: var(--accent-2); font-weight:600; }

.graph-card{
  background: var(--bg-elev); border:1px solid var(--border); border-radius: var(--radius-lg);
  padding: 16px; margin-bottom: 20px; box-shadow: var(--shadow);
}
.graph-legend{ display:flex; gap:18px; font-size:.82rem; color: var(--text-dim); margin-bottom:10px; }
.graph-legend .dot{ display:inline-block; width:9px; height:9px; border-radius:50%; margin-right:6px; }
.dot-fn{ background: var(--accent); }
.dot-deriv{ background: var(--accent-2); }
#graphCanvas{ width:100%; height:auto; display:block; border-radius: var(--radius-sm); background: var(--bg-elev-2); }

.steps-card{
  background: var(--bg-elev); border:1px solid var(--border); border-radius: var(--radius-lg);
  padding: 18px 22px; box-shadow: var(--shadow);
}
.steps-card summary{ cursor:pointer; font-weight:600; font-family: var(--font-display); }
.steps-list{ margin-top:14px; padding-left: 20px; color: var(--text-dim); }
.steps-list li{ margin-bottom: 10px; font-size: .93rem; }
.steps-list code{ color: var(--accent-2); }

/* ===================== MORE TOOLS ===================== */
.more-tools{ padding: 50px 24px; background: var(--bg-elev); border-top:1px solid var(--border); border-bottom:1px solid var(--border); }
.more-tools-inner{ max-width: 1280px; margin:0 auto; }
.more-tools h2{ font-size: 1.5rem; margin-bottom: 18px; }
.tools-grid{ display:grid; grid-template-columns: repeat(5, 1fr); gap: 10px; }
.tools-grid a{
  padding: 12px 14px; background: var(--bg-elev-2); border:1px solid var(--border); border-radius: var(--radius-sm);
  font-size: .85rem; color: var(--text-dim); transition: all .18s;
}
.tools-grid a:hover{ color: var(--text); border-color: var(--accent); transform: translateY(-2px); }

/* ===================== FEATURES ===================== */
.features{ padding: 70px 24px; }
.features-inner{ max-width: 1280px; margin:0 auto; }
.features h2{ font-size: 2rem; }
.features-grid{ display:grid; grid-template-columns: repeat(3, 1fr); gap: 20px; margin-top: 30px; }
.feature-card{
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius-md);
  padding: 24px; transition: transform .2s, border-color .2s;
}
.feature-card:hover{ transform: translateY(-3px); border-color: var(--accent); }
.feature-icon{
  width: 44px; height: 44px; display:flex; align-items:center; justify-content:center;
  background: linear-gradient(135deg, rgba(91,140,255,.15), rgba(34,211,201,.15));
  color: var(--accent-2); border-radius: 12px; font-size: 1.2rem; font-weight:700; margin-bottom: 14px;
}
.feature-card h3{ font-size: 1.08rem; margin-bottom:.4em; }
.feature-card p{ font-size:.92rem; margin:0; }

/* ===================== HOW IT WORKS ===================== */
.how-it-works{ padding: 70px 24px; background: var(--bg-elev); border-top:1px solid var(--border); border-bottom:1px solid var(--border); }
.how-inner{ max-width: 1280px; margin:0 auto; }
.how-inner h2{ font-size:2rem; margin-bottom: 30px; }
.how-grid{ display:grid; grid-template-columns: repeat(4, 1fr); gap: 20px; }
.how-num{
  display:inline-flex; align-items:center; justify-content:center; width:34px; height:34px;
  border-radius:50%; background: var(--bg-elev-2); border: 1px solid var(--border); color: var(--accent);
  font-family: var(--font-display); font-weight:700; margin-bottom: 12px;
}
.how-step h3{ font-size: 1.02rem; }
.how-step p{ font-size:.9rem; margin:0; }

/* ===================== ARTICLE ===================== */
.article-section{ padding: 70px 24px; }
.article-inner{ max-width: 780px; margin:0 auto; }
.article-inner h2{ font-size: 1.9rem; }
.article-inner h3{ font-size: 1.2rem; margin-top: 1.6em; }
.article-inner p{ font-size: .98rem; }

/* ===================== FAQ ===================== */
.faq-section{ padding: 70px 24px; background: var(--bg-elev); border-top:1px solid var(--border); border-bottom:1px solid var(--border); }
.faq-inner{ max-width: 780px; margin:0 auto; }
.faq-inner h2{ font-size: 1.9rem; margin-bottom: 24px; }
.faq-item{ border-bottom: 1px solid var(--border); }
.faq-question{
  width:100%; text-align:left; background:none; border:none; padding: 18px 0; cursor:pointer;
  display:flex; align-items:center; justify-content:space-between; font-size:1rem; font-weight:600; color: var(--text);
}
.faq-plus{ color: var(--accent); font-size:1.3rem; transition: transform .2s; flex-shrink:0; margin-left:12px; }
.faq-question[aria-expanded="true"] .faq-plus{ transform: rotate(45deg); }
.faq-answer{ max-height:0; overflow:hidden; transition: max-height .25s ease; }
.faq-question[aria-expanded="true"] + .faq-answer{ max-height: 260px; }
.faq-answer p{ padding-bottom: 18px; margin:0; font-size:.92rem; }

/* ===================== CTA ===================== */
.cta-section{ padding: 70px 24px; text-align:center; }
.cta-inner{ max-width: 640px; margin:0 auto; }
.cta-inner h2{ font-size: 2rem; }
.cta-buttons{ display:flex; justify-content:center; gap:14px; margin-top: 22px; flex-wrap:wrap; }

/* ===================== FOOTER ===================== */
.site-footer{ background: var(--bg-elev); border-top: 1px solid var(--border); padding: 50px 24px 0; }
.footer-inner{ max-width: 1280px; margin: 0 auto; display:grid; grid-template-columns: 1.6fr repeat(4, 1fr); gap: 30px; padding-bottom: 30px; }
.footer-col h4{ font-size:.85rem; text-transform:uppercase; letter-spacing:.04em; color: var(--text-faint); margin-bottom: 14px; }
.footer-col a{ display:block; font-size:.88rem; color: var(--text-dim); padding: 5px 0; }
.footer-col a:hover{ color: var(--accent); }
.footer-brand p{ font-size:.85rem; }
.footer-disclaimer{ font-size:.76rem; color: var(--text-faint); margin-top: 12px; }
.footer-bottom{ border-top:1px solid var(--border); padding: 18px 24px; text-align:center; font-size:.82rem; color: var(--text-faint); }

/* ===================== COOKIE BANNER ===================== */
.cookie-banner{
  position: fixed; bottom: 18px; left: 18px; right: 18px; max-width: 480px; margin: 0 auto;
  background: var(--bg-elev); border: 1px solid var(--border); border-radius: var(--radius-md);
  padding: 16px 18px; box-shadow: var(--shadow); z-index: 200;
  display:flex; flex-direction:column; gap: 12px; align-items:flex-start;
}
.cookie-banner p{ margin:0; font-size:.85rem; color: var(--text-dim); }
.cookie-banner a{ color: var(--accent); }
.cookie-banner[hidden]{ display:none; }

/* ===================== RESPONSIVE ===================== */
@media (max-width: 980px){
  .hero-inner{ grid-template-columns: 1fr; }
  .hero-visual{ order:-1; max-width: 320px; margin: 0 auto; }
  .features-grid{ grid-template-columns: repeat(2,1fr); }
  .how-grid{ grid-template-columns: repeat(2,1fr); }
  .footer-inner{ grid-template-columns: repeat(2,1fr); }
  .tools-grid{ grid-template-columns: repeat(3, 1fr); }
}

@media (max-width: 760px){
  .main-nav{
    position: fixed; top: var(--header-h); left:0; right:0; bottom:0;
    background: var(--bg); border-top: 1px solid var(--border);
    flex-direction:column; align-items:stretch; padding: 16px; gap: 4px;
    transform: translateX(100%); transition: transform .25s ease; overflow-y:auto;
    z-index: 90;
  }
  .main-nav.open{ transform: translateX(0); }
  .nav-link{ width:100%; justify-content:space-between; }
  .dropdown-panel{ position:static; width:100%; transform:none; grid-template-columns: 1fr; box-shadow:none; margin-top:4px; opacity:1; visibility:visible; display:none; }
  .nav-item.has-dropdown.open .dropdown-panel{ display:grid; }
  .nav-toggle{ display:flex; }
  .field-row{ grid-template-columns: 1fr; }
  .tools-grid{ grid-template-columns: repeat(2, 1fr); }
  .features-grid, .how-grid{ grid-template-columns: 1fr; }
  .footer-inner{ grid-template-columns: 1fr; }
  .hero{ padding: 44px 16px 30px; }
  .solver-section, .results-section, .features, .how-it-works, .article-section, .faq-section, .cta-section, .more-tools{ padding-left: 16px; padding-right: 16px; }
  .header-inner{ padding: 0 16px; }
}

@media (max-width: 420px){
  .cookie-banner{ left:10px; right:10px; }
  .btn-lg{ width:100%; }
  .cta-buttons .btn{ width:100%; }
}

/* prevent any horizontal overflow globally */
html, body{ max-width: 100%; }
.hero-inner, .solver-inner, .results-inner, .features-inner, .how-inner, .article-inner, .faq-inner, .cta-inner, .footer-inner, .more-tools-inner, .header-inner, .breadcrumb, .share-inner{
  width: 100%;
}