:root{
  --bg:#060E1C;--bg2:#0A1628;--panel:#0E1D33;--panel2:#13243F;
  --ink:#E5EEF8;--muted:#8FA6C0;--line:#1E3354;
  --cyan:#22D3EE;--amber:#FCD34D;--red:#F87171;--green:#34D399;--violet:#A78BFA;
}
*,*::before,*::after{box-sizing:border-box}
html{scroll-behavior:smooth}
body{margin:0;background:var(--bg);color:var(--ink);font-family:"Manrope","Inter",system-ui,"Segoe UI",Roboto,sans-serif;line-height:1.65;-webkit-font-smoothing:antialiased}
h1,h2,h3,h4{font-weight:700;line-height:1.25;margin:0 0 .4em}
h1{font-size:clamp(26px,4vw,40px)}
h2{font-size:clamp(20px,3vw,28px)}
h3{font-size:18px}h4{font-size:16px}
code,.mono{font-family:"JetBrains Mono",monospace}
a{color:var(--cyan);text-decoration:none}
a:hover{text-decoration:underline}
p{margin:0 0 1em}
b,strong{font-weight:700}

/* ── topnav ── */
.topnav{max-width:1160px;margin:14px auto 0;padding:0 20px}
.nav-back{display:inline-flex;align-items:center;gap:7px;text-decoration:none;font-family:"JetBrains Mono",monospace;font-size:13px;padding:7px 14px;border-radius:9px;border:1px solid var(--line);background:var(--panel);color:var(--muted)}
.nav-back:hover{border-color:var(--cyan);color:var(--cyan);background:rgba(34,211,238,.06)}

/* ── header ── */
header{max-width:1160px;margin:24px auto 0;padding:0 20px}
header .tag{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--cyan);text-transform:uppercase;letter-spacing:.08em;margin-bottom:8px}
header h1{margin-bottom:10px}
header p{color:var(--muted);font-size:15px;max-width:720px}

/* ── rail ── */
.railwrap{max-width:1160px;margin:22px auto 0;padding:0 20px}
.rail{display:flex;gap:8px;overflow-x:auto;padding-bottom:6px}
.rail a{flex:0 0 auto;display:flex;flex-direction:column;gap:2px;padding:10px 14px;border-radius:10px;border:1px solid var(--line);background:var(--panel);text-decoration:none;min-width:140px;transition:border-color .2s,background .2s}
.rail a:hover{border-color:var(--cyan)}
.rail a.cur{border-color:var(--cyan);background:linear-gradient(135deg,rgba(34,211,238,.08),rgba(34,211,238,.02))}
.rail a.done::after{content:" ✓";color:var(--green);font-size:12px}
.rail a .rn{font-family:"JetBrains Mono",monospace;font-size:11px;color:var(--cyan);text-transform:uppercase;letter-spacing:.06em}
.rail a .rt{font-size:13px;color:var(--ink);font-weight:600}

/* ── wrap ── */
.wrap{max-width:1160px;margin:0 auto;padding:24px 20px 0}

/* ── intro ── */
.intro{background:var(--panel);border-left:4px solid var(--amber);border-radius:12px;padding:20px 24px;margin-bottom:28px}
.intro .hook{font-size:16px;font-weight:600;margin-bottom:8px}
.intro p{color:var(--muted);margin:0}

/* ── section ── */
.section{margin-top:46px}
.sec-head{display:flex;align-items:center;gap:12px;margin-bottom:6px}
.sec-num{font-family:"JetBrains Mono",monospace;font-size:13px;color:var(--cyan);border:1px solid var(--cyan);border-radius:8px;padding:4px 10px;letter-spacing:.04em}
.sec-sub{color:var(--muted);font-size:14px;margin:0 0 10px}

/* ── badges ── */
.badges{display:flex;flex-wrap:wrap;gap:6px;margin-bottom:14px}
.b{font-family:"JetBrains Mono",monospace;font-size:11px;padding:3px 9px;border-radius:999px;text-transform:uppercase;letter-spacing:.04em}
.b.fgos{background:rgba(52,211,153,.12);color:var(--green)}
.b.fop{background:rgba(167,139,250,.12);color:var(--violet)}
.b.exam{background:rgba(252,211,77,.12);color:var(--amber)}

/* ── theory card ── */
.theory{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:22px 26px}
.theory h4{color:var(--cyan);border-left:3px solid var(--cyan);padding-left:10px;margin:18px 0 8px}
.theory h4:first-child{margin-top:0}
.theory code{background:var(--bg2);color:var(--amber);padding:2px 6px;border-radius:4px;font-size:.9em}

/* ── callout ── */
.callout{background:var(--bg2);border-left:3px solid var(--violet);border-radius:8px;padding:14px 18px;margin:14px 0}
.callout .ct{font-family:"JetBrains Mono",monospace;font-size:11px;color:var(--violet);text-transform:uppercase;letter-spacing:.06em;display:block;margin-bottom:4px}
.callout.amber{border-color:var(--amber)}.callout.amber .ct{color:var(--amber)}
.callout.cyan{border-color:var(--cyan)}.callout.cyan .ct{color:var(--cyan)}
.callout.green{border-color:var(--green)}.callout.green .ct{color:var(--green)}
.callout.red{border-color:var(--red)}.callout.red .ct{color:var(--red)}

/* ── figure ── */
.fig{background:var(--bg2);border:1px solid var(--line);border-radius:10px;padding:16px;margin:16px 0;text-align:center}
.fig svg{max-width:100%;height:auto}
.fig .cap{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--muted);margin-top:8px;text-align:left}

/* ── table ── */
.tblbox{overflow-x:auto;margin:14px 0}
table.dt{width:100%;border-collapse:collapse;font-size:14px}
table.dt th{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--cyan);text-transform:uppercase;letter-spacing:.04em;text-align:left;padding:10px 12px;border-bottom:2px solid var(--line);background:var(--bg2)}
table.dt td{padding:10px 12px;border-bottom:1px solid var(--line);vertical-align:top}
table.dt tr:last-child td{border-bottom:none}
table.dt tr:hover td{background:rgba(34,211,238,.03)}

/* ── analogy grid ── */
.agrid{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:12px;margin:14px 0}
.acard{background:var(--panel2);border:1px solid var(--line);border-radius:10px;padding:16px}
.acard .ico{font-size:28px;margin-bottom:6px}
.acard h5{margin:0 0 4px;font-size:15px}
.acard .ana{font-family:"JetBrains Mono",monospace;font-size:11px;color:var(--amber);margin-bottom:6px}
.acard p{font-size:13px;color:var(--muted);margin:0}

/* ── interactive shell ── */
.iv{background:var(--panel);border:1px solid var(--line);border-radius:14px;margin-top:28px;overflow:hidden}
.iv-head{display:flex;align-items:center;gap:12px;padding:16px 22px;border-bottom:1px solid var(--line);background:linear-gradient(180deg,var(--panel2),var(--panel))}
.iv-ico{font-size:26px}
.iv-t h3{margin:0;font-size:17px}
.iv-t .iv-s{font-size:12px;color:var(--muted);margin-top:2px}
.iv-tag{margin-left:auto;font-family:"JetBrains Mono",monospace;font-size:11px;color:var(--cyan);border:1px solid var(--cyan);border-radius:6px;padding:3px 8px}
.iv-body{padding:20px 22px}

/* ── buttons ── */
.btn{display:inline-flex;align-items:center;gap:6px;padding:9px 18px;border-radius:9px;border:1px solid var(--line);background:var(--panel2);color:var(--ink);font-size:14px;font-weight:600;cursor:pointer;transition:all .15s}
.btn:hover{border-color:var(--cyan);color:var(--cyan)}
.btn.primary{background:var(--cyan);color:#04222b;border-color:var(--cyan)}
.btn.primary:hover{filter:brightness(1.1)}
.btnrow{display:flex;flex-wrap:wrap;gap:8px;margin-top:14px}

/* ── feedback ── */
.feed{margin-top:12px;padding:12px 16px;border-radius:8px;font-size:14px;display:none}
.feed.show{display:block}
.feed.ok{background:rgba(52,211,153,.1);border:1px solid var(--green);color:var(--green)}
.feed.err{background:rgba(248,113,113,.1);border:1px solid var(--red);color:var(--red)}
.feed.info{background:rgba(34,211,238,.08);border:1px solid var(--cyan);color:var(--ink)}

/* ── modnav ── */
.modnav{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:14px;max-width:1160px;margin:38px auto 40px;padding:18px;border:1px solid var(--line);border-radius:14px;background:linear-gradient(180deg,var(--panel),var(--bg2))}
.modnav .mn-label{font-family:"JetBrains Mono",monospace;font-size:11px;color:var(--muted);text-transform:uppercase;letter-spacing:.06em;margin-bottom:4px}
.modnav .mn-title{font-size:15px;color:var(--ink);font-weight:700}
.nav-next{display:inline-flex;align-items:center;gap:9px;text-decoration:none;padding:12px 20px;border-radius:11px;background:var(--cyan);color:#04222b;font-weight:700;font-size:14px}
.nav-next:hover{filter:brightness(1.08)}
.nav-prev{display:inline-flex;align-items:center;gap:7px;text-decoration:none;font-family:"JetBrains Mono",monospace;font-size:13px;padding:9px 16px;border-radius:9px;border:1px solid var(--line);background:var(--panel2);color:var(--muted)}
.nav-prev:hover{border-color:var(--cyan);color:var(--cyan)}

/* ── protocol explorer ── */
.proto-stack{display:flex;flex-direction:column;gap:0;margin:14px 0}
.proto-layer{padding:14px 18px;border:1px solid var(--line);cursor:pointer;transition:all .2s}
.proto-layer:first-child{border-radius:10px 10px 0 0}
.proto-layer:last-child{border-radius:0 0 10px 10px}
.proto-layer:not(:first-child){border-top:none}
.proto-layer:hover,.proto-layer.active{background:rgba(34,211,238,.06);border-color:var(--cyan)}
.proto-layer .pl-name{font-weight:700;font-size:15px;color:var(--cyan)}
.proto-layer .pl-protos{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--amber);margin-top:2px}
.proto-layer .pl-desc{font-size:13px;color:var(--muted);margin-top:4px;display:none}
.proto-layer.active .pl-desc{display:block}

/* ── tcp handshake ── */
.hs-wrap{position:relative;padding:20px 0}
.hs-step{display:flex;align-items:center;gap:14px;padding:12px 16px;border-radius:10px;border:1px solid var(--line);margin-bottom:10px;opacity:.4;transition:all .3s}
.hs-step.active{opacity:1;border-color:var(--cyan);background:rgba(34,211,238,.06)}
.hs-step.done{opacity:.7;border-color:var(--green)}
.hs-arrow{font-size:24px;color:var(--cyan);min-width:40px;text-align:center}
.hs-label{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--amber)}
.hs-desc{font-size:13px;color:var(--muted)}

/* ── dns explorer ── */
.dns-tree{position:relative;padding:10px 0}
.dns-node{display:flex;align-items:center;gap:10px;padding:10px 14px;border-radius:8px;border:1px solid var(--line);margin:6px 0;cursor:pointer;transition:all .2s}
.dns-node:hover,.dns-node.active{border-color:var(--cyan);background:rgba(34,211,238,.06)}
.dns-node .dn-type{font-family:"JetBrains Mono",monospace;font-size:11px;padding:2px 8px;border-radius:4px;background:var(--panel2);color:var(--amber);min-width:40px;text-align:center}
.dns-node .dn-name{font-weight:600;font-size:14px}
.dns-node .dn-val{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--muted);margin-left:auto}

/* ── web builder ── */
.wb-wrap{display:grid;grid-template-columns:1fr 1fr;gap:16px}
.wb-code{background:#0d1117;border:1px solid var(--line);border-radius:10px;padding:16px;font-family:"JetBrains Mono",monospace;font-size:13px;line-height:1.6;overflow-x:auto;white-space:pre-wrap;color:#c9d1d9}
.wb-preview{background:#fff;border-radius:10px;padding:20px;color:#1a1a1a;font-size:14px;min-height:200px}
.wb-preview h1,.wb-preview h2,.wb-preview h3{color:#1a1a1a}
.wb-preview a{color:#0366d6}
.wb-tabs{display:flex;gap:4px;margin-bottom:10px}
.wb-tab{padding:6px 14px;border-radius:8px 8px 0 0;border:1px solid var(--line);background:var(--panel);font-size:13px;cursor:pointer;color:var(--muted)}
.wb-tab.active{background:var(--panel2);color:var(--cyan);border-bottom-color:var(--panel2)}

/* ── quest ── */
.quest{background:var(--panel);border:1px solid var(--line);border-radius:14px;padding:22px;margin-top:20px}
.q{margin-bottom:18px;padding:16px;border-radius:10px;border:1px solid var(--line);background:var(--bg2)}
.q p{font-weight:600;margin-bottom:10px}
.q .ans{display:block;width:100%;padding:10px 14px;border-radius:8px;border:1px solid var(--line);background:var(--panel);color:var(--ink);font-size:14px;cursor:pointer;margin-bottom:6px;text-align:left;transition:all .15s}
.q .ans:hover{border-color:var(--cyan)}
.q .ans.correct{border-color:var(--green);background:rgba(52,211,153,.1);color:var(--green)}
.q .ans.wrong{border-color:var(--red);background:rgba(248,113,113,.1);color:var(--red)}
.q .xp{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--amber);margin-top:6px}

/* ── exam test ── */
.testbar{display:flex;align-items:center;gap:12px;padding:12px 16px;background:var(--panel2);border-radius:10px;margin-bottom:16px}
.testbar .tb-score{font-family:"JetBrains Mono",monospace;font-size:14px;color:var(--cyan)}
.testbar .tb-prog{flex:1;height:6px;background:var(--line);border-radius:3px;overflow:hidden}
.testbar .tb-fill{height:100%;background:var(--cyan);border-radius:3px;transition:width .3s}

/* ── ext task ── */
.ext{background:var(--panel);border:1px solid var(--line);border-radius:12px;padding:22px;margin-top:20px}
.ext textarea{width:100%;min-height:140px;padding:12px;border-radius:8px;border:1px solid var(--line);background:var(--bg2);color:var(--ink);font-family:"Manrope",sans-serif;font-size:14px;resize:vertical}

/* ── logo carousel ── */
.logo-carousel{overflow:hidden;position:relative;margin:16px 0;padding:10px 0}
.logo-track{display:flex;gap:20px;animation:logoscroll 30s linear infinite}
.logo-carousel:hover .logo-track{animation-play-state:paused}
.logo-item{flex:0 0 auto;display:flex;flex-direction:column;align-items:center;gap:6px;padding:10px 14px;border-radius:10px;border:1px solid var(--line);background:var(--panel);min-width:100px}
.logo-item img{width:40px;height:40px;object-fit:contain}
.logo-item span{font-size:11px;color:var(--muted);text-align:center}
@keyframes logoscroll{0%{transform:translateX(0)}100%{transform:translateX(-50%)}}

/* ── encapsulation matryoshka ── */
.encap-wrap{display:flex;flex-direction:column;gap:6px}
.encap-layer{background:var(--bg2);border:1px solid var(--line);border-radius:10px;padding:14px 18px;cursor:pointer;transition:all .2s}
.encap-layer:hover{border-color:var(--cyan);background:rgba(34,211,238,.05)}
.encap-layer.active{border-color:var(--cyan);background:rgba(34,211,238,.08)}
.el-head{display:flex;align-items:center;gap:10px;font-weight:600;font-size:15px}
.el-badge{display:inline-block;padding:2px 8px;border-radius:6px;font-family:"JetBrains Mono",monospace;font-size:11px;font-weight:700;color:#fff}
.el-detail{display:none;margin-top:12px;padding-top:12px;border-top:1px solid var(--line)}
.encap-layer.active .el-detail{display:block}
.el-field{font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--muted);margin-bottom:6px;line-height:1.5}
.el-field b{color:var(--ink)}
.el-field code{background:var(--panel);padding:2px 6px;border-radius:4px;color:var(--cyan)}

/* ── build HTTP request ── */
.http-build{display:grid;grid-template-columns:1fr 1fr;gap:16px}
.hb-pool{display:flex;flex-direction:column;gap:8px}
.hb-frag{padding:10px 14px;background:var(--panel);border:1px solid var(--line);border-radius:8px;font-family:"JetBrains Mono",monospace;font-size:12px;color:var(--ink);cursor:grab;transition:all .15s}
.hb-frag:hover{border-color:var(--cyan);background:var(--panel2)}
.hb-frag.dragging{opacity:.5}
.hb-frag.placed{opacity:.4;pointer-events:none}
.hb-frag.selected{border-color:var(--cyan);background:rgba(34,211,238,.12);box-shadow:0 0 0 2px rgba(34,211,238,.3)}
.hb-target{display:flex;flex-direction:column;gap:6px}
.hb-slot{padding:12px 14px;background:var(--bg2);border:2px dashed var(--line);border-radius:8px;font-size:13px;color:var(--muted);display:flex;align-items:center;gap:10px;min-height:44px;transition:all .15s}
.hb-slot.drag-over{border-color:var(--cyan);background:rgba(34,211,238,.08)}
.hb-slot.filled{border-style:solid;border-color:var(--green);background:rgba(52,211,153,.05)}
.hb-slot.wrong{border-color:var(--red);background:rgba(248,113,113,.05)}
.hs-num{display:inline-flex;align-items:center;justify-content:center;width:24px;height:24px;border-radius:50%;background:var(--panel);border:1px solid var(--line);font-family:"JetBrains Mono",monospace;font-size:12px;font-weight:700;color:var(--cyan);flex-shrink:0}
.hb-slot.filled .hs-num{background:var(--green);color:#fff;border-color:var(--green)}
.hb-slot.wrong .hs-num{background:var(--red);color:#fff;border-color:var(--red)}
@media(max-width:640px){.http-build{grid-template-columns:1fr}}

/* ── responsive ── */
@media(max-width:880px){
  .wb-wrap{grid-template-columns:1fr}
}

/* ── Port Quiz ── */
.pq-wrap{display:flex;flex-direction:column;gap:12px}
.pq-q{padding:14px;background:var(--panel);border:1px solid var(--line);border-radius:10px}
.pq-port{font-family:"JetBrains Mono",monospace;font-size:18px;color:var(--cyan);margin-bottom:10px}
.pq-opts{display:flex;flex-wrap:wrap;gap:8px}
.pq-opt{padding:8px 16px;background:var(--bg2);border:1px solid var(--line);border-radius:8px;font-family:"JetBrains Mono",monospace;font-size:13px;color:var(--ink);cursor:pointer;transition:all .15s}
.pq-opt:hover:not(.disabled){border-color:var(--cyan);background:var(--panel2)}
.pq-opt.correct{border-color:var(--green);background:rgba(52,211,153,.15);color:var(--green)}
.pq-opt.wrong{border-color:var(--red);background:rgba(248,113,113,.1);color:var(--red)}
.pq-opt.disabled{opacity:.6;cursor:default;pointer-events:none}
.pq-feed{margin-top:10px;font-size:13px;color:var(--muted);display:none}
.pq-feed.show{display:block}

@media(max-width:560px){
  .btn{min-height:44px}
  .modnav{flex-direction:column;align-items:stretch;text-align:center}
  .nav-prev,.nav-next{justify-content:center}
  table.dt{font-size:13px}
  table.dt th,table.dt td{padding:8px}
  .iv-head{flex-wrap:wrap}
  .iv-tag{margin-left:0}
  .proto-layer{padding:10px 14px}
  .hs-step{flex-direction:column;text-align:center}
}