/* TechPath Networks — shared styles for the landing page and every article. */
*{margin:0;padding:0;box-sizing:border-box}
:root{--navy:#0b1f3a;--blue:#1565c0;--teal:#00897b;--ink:#1f2937;--muted:#6b7280;--line:#e5e7eb;--bg:#f5f7fb}
body{font-family:'Segoe UI',system-ui,-apple-system,sans-serif;color:var(--ink);background:var(--bg);line-height:1.65}
a{color:var(--blue)}

/* Top bar with the tabs */
.topbar{position:sticky;top:0;z-index:50;background:var(--navy);color:#fff;display:flex;align-items:center;
  justify-content:space-between;flex-wrap:wrap;gap:.5rem;padding:.7rem 1.5rem;box-shadow:0 2px 10px rgba(0,0,0,.2)}
.brand{display:flex;align-items:center;gap:.6rem;color:#fff;text-decoration:none;font-weight:700;letter-spacing:.5px;font-size:1.15rem}
.brand svg{flex:none}
.tabs{display:flex;gap:.3rem;flex-wrap:wrap}
.tab{color:#cfd8e3;text-decoration:none;font-weight:600;font-size:.95rem;padding:.5rem 1rem;border-radius:8px;transition:.15s}
.tab:hover{background:rgba(255,255,255,.08);color:#fff}
.tab.active{background:#fff;color:var(--navy)}
.tab.study{background:#ffd54f;color:#1a237e}
.tab.study:hover{background:#ffe082}

.wrap{max-width:1000px;margin:0 auto;padding:2rem 1.5rem}

/* Landing */
.hero{background:url(img/hero-network.svg) center/cover no-repeat,linear-gradient(135deg,var(--navy),var(--blue));color:#fff;padding:4.5rem 1.5rem 4rem;text-align:center}
.hero h1{font-size:2.6rem;margin-bottom:.4rem}
.hero p{font-size:1.15rem;opacity:.9;max-width:640px;margin:0 auto}
.choices{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:1.5rem;margin-top:-2.2rem}
.choice{background:#fff;border-radius:14px;padding:1.8rem;box-shadow:0 6px 24px rgba(11,31,58,.12);text-decoration:none;color:var(--ink);
  border-top:5px solid var(--blue);transition:.2s;display:block}
.choice:hover{transform:translateY(-3px);box-shadow:0 10px 30px rgba(11,31,58,.18)}
.choice.study{border-top-color:#ffb300}
.choice .art{display:block;width:calc(100% + 3.6rem);margin:-1.8rem -1.8rem 1rem;border-radius:9px 9px 0 0;aspect-ratio:400/220;object-fit:cover}
.choice .icon{font-size:2.4rem}
.choice h2{font-size:1.35rem;margin:.5rem 0 .4rem;color:var(--navy)}
.choice p{color:var(--muted)}
.choice .go{display:inline-block;margin-top:1rem;font-weight:700;color:var(--blue)}
.choice.study .go{color:#e65100}

/* Library */
.panel{display:none}
.panel.active{display:block}
.section-title{font-size:1.6rem;color:var(--navy);margin-bottom:.3rem}
.lead{color:var(--muted);margin-bottom:1.3rem}
.filters{display:flex;gap:.4rem;flex-wrap:wrap;margin-bottom:1.2rem}
.filter{border:1.5px solid var(--line);background:#fff;border-radius:999px;padding:.35rem .9rem;font:inherit;font-size:.85rem;
  font-weight:600;color:var(--muted);cursor:pointer}
.filter.active{border-color:var(--blue);background:var(--blue);color:#fff}
.cards{display:grid;grid-template-columns:repeat(auto-fit,minmax(280px,1fr));gap:1.2rem}
.card{background:#fff;border-radius:12px;padding:1.4rem;box-shadow:0 2px 12px rgba(0,0,0,.06);text-decoration:none;color:var(--ink);
  display:flex;flex-direction:column;transition:.15s;border:1px solid transparent}
.card:hover{border-color:var(--blue)}
.card .thumb{display:block;width:calc(100% + 2.8rem);margin:-1.4rem -1.4rem .9rem;border-radius:12px 12px 0 0;aspect-ratio:400/180;object-fit:cover}
.card{overflow:hidden}
.card h3{color:var(--navy);margin:.4rem 0}
.card p{color:var(--muted);font-size:.93rem;flex:1}
.meta{font-size:.78rem;color:var(--muted);margin-top:.8rem}
.tag{display:inline-block;font-size:.72rem;font-weight:700;text-transform:uppercase;letter-spacing:.05em;padding:.15rem .55rem;
  border-radius:4px;background:#e3f2fd;color:var(--blue)}
.tag.routing{background:#e0f2f1;color:var(--teal)}
.tag.addressing{background:#fff3e0;color:#e65100}
.tag.interconnect{background:#f1f8e9;color:#558b2f}

/* Article */
article{background:#fff;border-radius:14px;padding:2.2rem 2.4rem;box-shadow:0 2px 14px rgba(0,0,0,.06)}
article h1{font-size:2rem;color:var(--navy);margin:.4rem 0 .3rem;line-height:1.25}
article .byline{color:var(--muted);font-size:.88rem;margin-bottom:1.2rem}
article .lead-img{display:block;width:100%;max-width:640px;margin:0 auto 1.6rem;border-radius:12px}
article h2{font-size:1.35rem;color:var(--navy);margin:2rem 0 .6rem}
article h3{font-size:1.08rem;margin:1.3rem 0 .4rem}
article p{margin-bottom:.9rem}
article ul,article ol{margin:0 0 1rem 1.4rem}
article li{margin-bottom:.35rem}
article code{font-family:'SFMono-Regular',Consolas,monospace;background:#f1f5f9;padding:.1rem .35rem;border-radius:4px;font-size:.9em}
article pre{background:#0f172a;color:#e2e8f0;padding:1rem 1.2rem;border-radius:10px;overflow-x:auto;margin:0 0 1.1rem;font-size:.88rem;line-height:1.5}
article pre code{background:none;padding:0;color:inherit}
article table{width:100%;border-collapse:collapse;margin:0 0 1.2rem;font-size:.92rem}
article th,article td{border:1px solid var(--line);padding:.55rem .7rem;text-align:left;vertical-align:top}
article th{background:var(--navy);color:#fff}
article tr:nth-child(even) td{background:#f8fafc}
.note{background:#e3f2fd;border-left:4px solid var(--blue);border-radius:8px;padding:.9rem 1.1rem;margin:1rem 0}
.warn{background:#fff3e0;border-left:4px solid #fb8c00;border-radius:8px;padding:.9rem 1.1rem;margin:1rem 0}
.back{display:inline-block;margin-bottom:1rem;font-weight:600;text-decoration:none}

footer{text-align:center;color:var(--muted);font-size:.85rem;padding:2rem 1rem}

@media (max-width:600px){.hero h1{font-size:2rem}article{padding:1.4rem}.topbar{padding:.6rem 1rem}}