:root{--bg:#f7faff;--panel:#fff;--panel-2:#f1f6ff;--text:#0f172a;--muted:#475569;--line:#dbe6f4;--brand:#2563eb;--brand-2:#38bdf8;--accent:#0ea5e9;--success:#0f766e;--shadow:0 16px 45px rgba(15,23,42,.08);--radius:22px;--radius-sm:14px;--wrap:min(1180px,calc(100% - 32px));scroll-behavior:smooth}*{box-sizing:border-box}html{margin:0;padding:0}body{margin:0;font:400 16px/1.65 Inter,ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;color:var(--text);background:linear-gradient(180deg,#f9fbff 0%,#f3f7fe 100%)}img{max-width:100%;height:auto}a{color:var(--brand);text-decoration:none}a:hover{text-decoration:underline}.wrap{width:var(--wrap);margin:auto}.narrow{max-width:900px}.skip-link{position:absolute;left:-9999px;top:auto}.skip-link:focus{left:12px;top:12px;z-index:1000;background:#fff;padding:10px 14px;border-radius:10px;box-shadow:var(--shadow)}.site-header{position:sticky;top:0;z-index:50;background:rgba(247,250,255,.88);backdrop-filter:blur(12px);border-bottom:1px solid rgba(219,230,244,.8)}.nav-wrap{display:flex;align-items:center;justify-content:space-between;gap:20px;padding:14px 0}.brand{display:flex;align-items:center;min-width:0}.site-nav{display:flex;gap:22px;flex-wrap:wrap}.site-nav a{font-weight:600;color:var(--text)}.nav-cta,.btn{display:inline-flex;align-items:center;justify-content:center;border:0;border-radius:999px;padding:13px 20px;font-weight:700;cursor:pointer;transition:.2s ease;min-height:46px}.nav-cta,.btn-primary{background:linear-gradient(135deg,var(--brand),var(--brand-2));color:#fff;box-shadow:0 12px 28px rgba(37,99,235,.22)}.btn-secondary{background:#fff;color:var(--text);border:1px solid var(--line)}.btn:hover,.nav-cta:hover{transform:translateY(-1px);text-decoration:none}.hero{padding:62px 0 28px}.hero-grid{display:grid;grid-template-columns:1.1fr .9fr;gap:28px;align-items:center}.eyebrow,.kicker{display:inline-flex;align-items:center;gap:8px;padding:6px 12px;border:1px solid var(--line);border-radius:999px;background:rgba(255,255,255,.9);font-size:.82rem;font-weight:700;color:var(--brand);letter-spacing:.03em;text-transform:uppercase}.hero h1{font-size:clamp(2.2rem,6vw,4.3rem);line-height:1.05;letter-spacing:-.03em;margin:16px 0 16px}.hero-copy,.section-head p,.info-card p,.examples-grid p,.faq-list p,.mistake-list p,.site-footer p{color:var(--muted)}.hero-list{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px 18px;padding:0;margin:22px 0;list-style:none}.hero-list li,.trust-row span{position:relative;padding-left:24px}.hero-list li:before,.trust-row span:before{content:"";position:absolute;left:0;top:10px;width:10px;height:10px;border-radius:999px;background:linear-gradient(135deg,var(--brand),var(--brand-2))}.hero-actions{display:flex;gap:12px;flex-wrap:wrap;margin:20px 0 16px}.trust-row{display:flex;flex-wrap:wrap;gap:14px 18px;font-size:.95rem;color:var(--muted)}.hero-card,.calculator-card,.result-card,.steps-card,.info-card,.table-card,.link-card,.examples-grid article,.mistake-list article{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow)}.hero-card{padding:26px}.hero-card h2,.section-head h2{font-size:clamp(1.6rem,3vw,2.6rem);line-height:1.12;letter-spacing:-.03em;margin:14px 0}.feature-grid,.rule-grid,.apps-grid,.cards-grid,.examples-grid,.mistake-list{display:grid;gap:18px}.feature-grid{grid-template-columns:repeat(2,minmax(0,1fr));margin-top:18px}.feature-grid article{background:var(--panel-2);padding:18px;border-radius:18px;border:1px solid var(--line)}.feature-grid p{margin:.4rem 0 0;color:var(--muted)}.section{padding:34px 0}.alt{background:linear-gradient(180deg,rgba(255,255,255,.55),rgba(240,246,255,.72))}.section-head{margin-bottom:22px}.calculator-shell{display:grid;grid-template-columns:minmax(0,430px) minmax(0,1fr);gap:22px;align-items:start}.calculator-card,.result-card,.steps-card,.table-card{padding:24px}.field-group{display:grid;gap:8px;margin-bottom:16px}.field-group label{font-weight:700}input,select{width:100%;padding:15px 16px;border-radius:16px;border:1px solid #cbd9ee;background:#fff;color:var(--text);font:inherit;outline:0}input:focus,select:focus{border-color:var(--brand);box-shadow:0 0 0 4px rgba(37,99,235,.12)}small{color:var(--muted)}.button-row{display:flex;gap:10px;flex-wrap:wrap}.error{margin-top:12px;color:#b91c1c;font-weight:700}.result-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}.result-grid article{padding:18px;border-radius:18px;background:var(--panel-2);border:1px solid var(--line)}.result-label{display:block;color:var(--muted);font-size:.92rem;margin-bottom:8px}.result-grid strong{display:block;font-size:1.18rem;line-height:1.35;word-break:break-word}.steps-header{display:flex;align-items:center;justify-content:space-between;gap:16px;padding-bottom:14px;border-bottom:1px solid var(--line);margin-bottom:14px}.steps-header span{color:var(--muted)}.steps-list{margin:0;padding-left:20px}.steps-list li+li{margin-top:10px}.rule-grid,.apps-grid{grid-template-columns:repeat(3,minmax(0,1fr))}.info-card{padding:22px}.info-card h3,.examples-grid h3,.mistake-list h3{margin:0 0 10px;font-size:1.08rem}.table-wrap{overflow:auto}.table-card h3{margin:0 0 16px}table{width:100%;border-collapse:collapse;min-width:680px}th,td{text-align:left;padding:14px 16px;border-bottom:1px solid var(--line);vertical-align:top}thead th{background:var(--panel-2);font-size:.95rem}.examples-grid{grid-template-columns:repeat(3,minmax(0,1fr))}.examples-grid article{padding:20px}.examples-grid strong{display:block;margin-top:12px;color:var(--success)}.mistake-list{grid-template-columns:repeat(2,minmax(0,1fr))}.mistake-list article{padding:20px}.faq-list{display:grid;gap:12px}.faq-list details{background:#fff;border:1px solid var(--line);border-radius:18px;padding:18px 20px}.faq-list summary{cursor:pointer;font-weight:700;list-style:none}.faq-list summary::-webkit-details-marker{display:none}.faq-list details[open]{box-shadow:var(--shadow)}.faq-list p{margin:12px 0 0}.cards-grid{grid-template-columns:repeat(3,minmax(0,1fr))}.link-card{display:grid;gap:8px;padding:22px;color:var(--text)}.link-card:hover{text-decoration:none;border-color:#bad0ef;transform:translateY(-2px)}.link-card span{color:var(--muted)}.site-footer{padding:26px 0 44px;border-top:1px solid var(--line);background:rgba(255,255,255,.72)}.footer-wrap{display:flex;justify-content:space-between;gap:24px;align-items:flex-start}.footer-wrap nav{display:grid;gap:10px}@media (max-width:1024px){.hero-grid,.calculator-shell,.rule-grid,.apps-grid,.examples-grid,.cards-grid,.mistake-list{grid-template-columns:1fr 1fr}.hero-grid{grid-template-columns:1fr}.feature-grid{grid-template-columns:1fr 1fr}}@media (max-width:760px){.nav-wrap{flex-wrap:wrap}.site-nav{order:3;width:100%;justify-content:flex-start;overflow:auto;padding-bottom:2px}.hero{padding-top:32px}.hero-list,.result-grid,.rule-grid,.apps-grid,.examples-grid,.cards-grid,.mistake-list,.feature-grid,.calculator-shell{grid-template-columns:1fr}.footer-wrap,.steps-header{flex-direction:column;align-items:flex-start}.button-row{display:grid;grid-template-columns:1fr}.btn,.nav-cta{width:100%}.section{padding:26px 0}.calculator-card,.result-card,.steps-card,.table-card,.hero-card{padding:20px}table{min-width:620px}}
/* Source-aligned calculator upgrades */
.calc-input{font-size:1.15rem;font-weight:600;letter-spacing:.01em}
.calculator-shell-source{align-items:start}
.calculator-card-source{gap:18px}
.field-grid{display:grid;grid-template-columns:1.1fr .9fr;gap:16px}
.field-group-wide{grid-column:1/-1}
.field-group-note{display:flex;flex-direction:column;justify-content:center;background:linear-gradient(180deg,#f7fbff,#edf5ff);border:1px solid var(--line);border-radius:18px;padding:16px 18px}
.field-group-note p{margin:6px 0 0;color:var(--muted)}
.keypad{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:10px}
.keypad-btn{appearance:none;border:1px solid var(--line);background:#fff;border-radius:16px;min-height:52px;padding:0 10px;font:700 1rem/1 Inter,ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Arial,sans-serif;color:var(--text);box-shadow:0 8px 22px rgba(15,23,42,.05);cursor:pointer;transition:transform .15s ease,box-shadow .15s ease,border-color .15s ease}
.keypad-btn:hover{transform:translateY(-1px);box-shadow:0 12px 28px rgba(15,23,42,.08);border-color:#bfd2ee}
.keypad-btn:focus-visible{outline:3px solid rgba(37,99,235,.2);outline-offset:2px}
.result-grid{grid-template-columns:repeat(3,minmax(0,1fr))}
.steps-list li{margin-bottom:10px}
@media (max-width:900px){.field-grid{grid-template-columns:1fr}.result-grid{grid-template-columns:repeat(2,minmax(0,1fr))}}
@media (max-width:640px){.keypad{grid-template-columns:repeat(4,minmax(0,1fr))}.result-grid{grid-template-columns:1fr}.button-row{flex-wrap:wrap}}

/* Centered calculator layout refinement */
.calc-wrap{max-width:860px}
#calculator .section-head{text-align:center;max-width:760px;margin:0 auto 22px}
.calculator-shell,.calculator-shell-source{display:grid;grid-template-columns:1fr;gap:22px;max-width:760px;margin:0 auto;align-items:stretch}
.calculator-card,.result-card{width:100%}
.calculator-card-source{padding:16px;background:#efefef;border-color:#d5d5d5;box-shadow:none;border-radius:12px}
.result-card-centered{padding:16px 18px;background:#f8f8f8;border-color:#d7d7d7;box-shadow:none;border-radius:12px}
#calculator input,#calculator select{border-radius:8px;border-color:#bdbdbd;background:#fff;box-shadow:none}
#calculator input{font-size:1.1rem;padding:16px 14px}
.field-group-note{background:#f2f2f2;border:1px solid #d3d3d3;border-radius:10px;padding:12px 14px}
.field-grid{grid-template-columns:1fr;gap:12px}
.keypad{grid-template-columns:repeat(5,minmax(0,1fr));gap:4px}
.keypad-btn{min-height:44px;border-radius:4px;border:1px solid #b7b7b7;background:#f7f7f7;box-shadow:none;color:#4b4b4b;font-weight:600}
.keypad-btn:hover{transform:none;box-shadow:none;border-color:#999}
.keypad-operator{background:#cc6a00;color:#fff;border-color:#b85f00}
.keypad-function{background:#f3f3f3;color:#505050}
.button-row-calc{display:grid;grid-template-columns:1.1fr 1fr 1fr 1.1fr;gap:4px}
.button-row-calc .btn{min-height:44px;border-radius:4px;padding:10px 12px;box-shadow:none}
.button-row-calc .btn-utility{background:#efefef;border:1px solid #b7b7b7;color:#555}
.button-row-calc .btn-solve{background:#88d43a;color:#1f2a0a;border:1px solid #73bb2f;font-weight:800}
.result-card-top{display:flex;align-items:center;justify-content:space-between;gap:12px;margin-bottom:14px}
.result-history-label{font-size:.86rem;font-weight:700;color:#757575;text-transform:uppercase;letter-spacing:.04em}
.btn-copy-inline{min-height:38px;padding:8px 14px;border-radius:999px}
.result-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}
.result-grid article{background:#fff;border:1px solid #e7c26b;border-radius:10px;padding:16px}
.result-grid strong{font-size:1.05rem}
#steps .wrap.narrow{max-width:760px}
.steps-card{background:#fff;border-color:#d8d8d8;box-shadow:none;border-radius:12px;padding:18px}
.steps-header{padding-bottom:12px;margin-bottom:12px}
@media (max-width:700px){
  .calc-wrap{max-width:none}
  .keypad{grid-template-columns:repeat(4,minmax(0,1fr))}
  .button-row-calc{grid-template-columns:repeat(2,minmax(0,1fr))}
  .result-card-top{align-items:flex-start;flex-direction:column}
  .result-grid{grid-template-columns:1fr}
}