/* ==========================================================================
   Fonts (self-hosted, SIL OFL): Lexend for reading, JetBrains Mono for the CLI
   ========================================================================== */
@font-face { font-family: 'Lexend'; font-weight: 400; font-display: swap; src: url('../fonts/lexend-vietnamese-400-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'Lexend'; font-weight: 400; font-display: swap; src: url('../fonts/lexend-latin-400-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }
@font-face { font-family: 'Lexend'; font-weight: 500; font-display: swap; src: url('../fonts/lexend-vietnamese-500-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'Lexend'; font-weight: 500; font-display: swap; src: url('../fonts/lexend-latin-500-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }
@font-face { font-family: 'Lexend'; font-weight: 600; font-display: swap; src: url('../fonts/lexend-vietnamese-600-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'Lexend'; font-weight: 600; font-display: swap; src: url('../fonts/lexend-latin-600-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }
@font-face { font-family: 'Lexend'; font-weight: 700; font-display: swap; src: url('../fonts/lexend-vietnamese-700-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'Lexend'; font-weight: 700; font-display: swap; src: url('../fonts/lexend-latin-700-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }
@font-face { font-family: 'JetBrains Mono'; font-weight: 400; font-display: swap; src: url('../fonts/jetbrains-mono-vietnamese-400-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'JetBrains Mono'; font-weight: 400; font-display: swap; src: url('../fonts/jetbrains-mono-latin-400-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }
@font-face { font-family: 'JetBrains Mono'; font-weight: 500; font-display: swap; src: url('../fonts/jetbrains-mono-vietnamese-500-normal.woff2') format('woff2'); unicode-range: U+0102-0103,U+0110-0111,U+0128-0129,U+0168-0169,U+01A0-01A1,U+01AF-01B0,U+0300-0301,U+0303-0304,U+0308-0309,U+0323,U+0329,U+1EA0-1EF9,U+20AB; }
@font-face { font-family: 'JetBrains Mono'; font-weight: 500; font-display: swap; src: url('../fonts/jetbrains-mono-latin-500-normal.woff2') format('woff2'); unicode-range: U+0000-00FF,U+0131,U+0152-0153,U+02BB-02BC,U+02C6,U+02DA,U+02DC,U+0304,U+0308,U+0329,U+2000-206F,U+20AC,U+2122,U+2191,U+2193,U+2212,U+2215,U+FEFF,U+FFFD; }

/* ==========================================================================
   Tokens. Palette from a network lab: cool paper, navy ink, Cisco console-cable
   blue, and one colour per learning phase.
   ========================================================================== */
:root {
  --paper: #F1F4F6;
  --card: #FFFFFF;
  --sunk: #E6ECF0;
  --ink: #13263A;
  --ink-2: #51637A;
  --line: #D5DEE6;
  --cable: #1B84C6;
  --cable-ink: #0F5F95;
  --cable-soft: #DCEEFA;
  --on-cable: #FFFFFF;

  --p-blue: #1B84C6;
  --p-green: #23936A;
  --p-amber: #C47F12;
  --p-violet: #7457C9;

  --ok: #1F8A5B;
  --ok-soft: #DDF2E7;
  --bad: #C2453A;
  --bad-soft: #F8E0DD;
  --warn-soft: #FBEFD6;
  --warn-ink: #85560A;

  --term-bg: #0E2233;
  --term-ink: #DCE6EF;
  --term-dim: #8FA6BA;
  --term-prompt: #7CC4F2;
  --term-err: #FF9B8F;
  --term-sys: #E8C46A;

  --font: 'Lexend', system-ui, -apple-system, 'Segoe UI', Roboto, sans-serif;
  --mono: 'JetBrains Mono', ui-monospace, 'Cascadia Mono', Consolas, monospace;
  --r: 8px;
  --r-lg: 14px;
  --wrap: 1180px;
  --gutter: 24px;
  --focus: 0 0 0 2px var(--paper), 0 0 0 4px var(--cable);
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #0F1A24; --card: #152330; --sunk: #1B2C3B; --ink: #E3EAF1; --ink-2: #9AABBD; --line: #26394B;
    --cable: #5FB3EA; --cable-ink: #8CCBF3; --cable-soft: #17344B; --on-cable: #08131D;
    --p-blue: #5FB3EA; --p-green: #4DC294; --p-amber: #E3A84A; --p-violet: #A891EC;
    --ok: #4DC294; --ok-soft: #133427; --bad: #F08A7F; --bad-soft: #3B1F1C; --warn-soft: #3A2D14; --warn-ink: #F1C677;
    --term-bg: #08141E;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --paper: #0F1A24; --card: #152330; --sunk: #1B2C3B; --ink: #E3EAF1; --ink-2: #9AABBD; --line: #26394B;
  --cable: #5FB3EA; --cable-ink: #8CCBF3; --cable-soft: #17344B; --on-cable: #08131D;
  --p-blue: #5FB3EA; --p-green: #4DC294; --p-amber: #E3A84A; --p-violet: #A891EC;
  --ok: #4DC294; --ok-soft: #133427; --bad: #F08A7F; --bad-soft: #3B1F1C; --warn-soft: #3A2D14; --warn-ink: #F1C677;
  --term-bg: #08141E;
  color-scheme: dark;
}
[data-phase="nen-tang"], [data-color="blue"] { --c: var(--p-blue); }
[data-phase="switching"], [data-color="green"] { --c: var(--p-green); }
[data-phase="routing"], [data-color="amber"] { --c: var(--p-amber); }
[data-phase="dich-vu"], [data-color="violet"] { --c: var(--p-violet); }

/* ==========================================================================
   Base
   ========================================================================== */
*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-padding-top: 84px; }
body { margin: 0; background: var(--paper); color: var(--ink); font: 400 1rem/1.65 var(--font); -webkit-font-smoothing: antialiased; }
h1, h2, h3, h4 { margin: 0; line-height: 1.2; letter-spacing: -0.01em; }
p { margin: 0 0 1em; }
ul, ol { margin: 0; padding: 0; }
a { color: var(--cable-ink); text-underline-offset: 3px; }
button, input, select, textarea { font: inherit; color: inherit; }
code, kbd, pre, .mono { font-family: var(--mono); font-size: 0.92em; }
:focus-visible { outline: none; box-shadow: var(--focus); border-radius: 6px; }
[hidden] { display: none !important; }
.muted { color: var(--ink-2); }
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }
.skip { position: absolute; top: -60px; left: 12px; z-index: 50; padding: 10px 14px; background: var(--cable); color: var(--on-cable); border-radius: var(--r); }
.skip:focus { top: 12px; }
.wrap { max-width: var(--wrap); margin: 0 auto; padding: 0 var(--gutter); }
@media (max-width: 640px) { :root { --gutter: 16px; } }

/* ==========================================================================
   Header
   ========================================================================== */
.top { position: sticky; top: 0; z-index: 30; background: color-mix(in srgb, var(--paper) 90%, transparent); backdrop-filter: blur(10px); -webkit-backdrop-filter: blur(10px); border-bottom: 1px solid var(--line); }
.top-inner { display: flex; align-items: center; gap: 20px; height: 64px; }
.brand { display: flex; align-items: center; gap: 10px; text-decoration: none; color: var(--ink); font-weight: 700; font-size: 1.0625rem; white-space: nowrap; }
.brand svg { width: 32px; height: 32px; flex: none; }
.nav { flex: 1; overflow-x: auto; scrollbar-width: none; }
.nav::-webkit-scrollbar { display: none; }
.nav ul { display: flex; gap: 2px; list-style: none; justify-content: flex-end; }
.nav a { display: block; padding: 8px 12px; border-radius: var(--r); color: var(--ink-2); text-decoration: none; font-size: 0.9375rem; font-weight: 500; white-space: nowrap; }
.nav a:hover { color: var(--ink); background: var(--sunk); }
.nav a[aria-current="page"] { color: var(--ink); background: var(--card); box-shadow: inset 0 0 0 1px var(--line); }
.icon-btn { display: grid; place-items: center; width: 40px; height: 40px; flex: none; border-radius: var(--r); border: 1px solid var(--line); background: var(--card); cursor: pointer; }
.icon-btn svg { width: 19px; height: 19px; }
.i-sun { display: none; }
:root[data-theme="dark"] .i-sun { display: block; }
:root[data-theme="dark"] .i-moon { display: none; }
@media (prefers-color-scheme: dark) { :root:not([data-theme="light"]) .i-sun { display: block; } :root:not([data-theme="light"]) .i-moon { display: none; } }
@media (max-width: 760px) {
  .brand span { display: none; }
  .top-inner { gap: 10px; }
  .nav ul { justify-content: flex-start; }
  .nav a { padding: 8px 9px; font-size: 0.875rem; }
}

/* ==========================================================================
   Buttons, inputs, chips
   ========================================================================== */
.btn { display: inline-flex; align-items: center; justify-content: center; gap: 8px; min-height: 44px; padding: 0 18px; border-radius: var(--r); border: 1px solid transparent; font-weight: 600; font-size: 0.9375rem; text-decoration: none; cursor: pointer; white-space: nowrap; transition: background-color .15s, border-color .15s; }
.btn-primary { background: var(--cable); color: var(--on-cable); }
.btn-primary:hover { background: color-mix(in srgb, var(--cable) 85%, var(--ink)); }
.btn-quiet { background: var(--card); color: var(--ink); border-color: var(--line); }
.btn-quiet:hover { border-color: var(--ink-2); }
.btn-ghost { background: transparent; color: var(--cable-ink); padding: 0 10px; }
.btn-ghost:hover { background: var(--cable-soft); }
.btn-sm { min-height: 36px; padding: 0 12px; font-size: 0.875rem; }
.btn[disabled] { opacity: .5; cursor: not-allowed; }
.row { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; }
input[type=text], input[type=number], select { min-height: 44px; padding: 8px 12px; border: 1px solid var(--line); border-radius: var(--r); background: var(--card); }
input[type=text]:focus-visible, select:focus-visible { border-color: var(--cable); }
select { appearance: none; padding-right: 34px; background-image: linear-gradient(45deg, transparent 50%, var(--ink-2) 50%), linear-gradient(135deg, var(--ink-2) 50%, transparent 50%); background-position: calc(100% - 17px) 50%, calc(100% - 12px) 50%; background-size: 5px 5px; background-repeat: no-repeat; cursor: pointer; }
label.check { display: inline-flex; align-items: center; gap: 8px; cursor: pointer; font-size: 0.9375rem; }
input[type=checkbox], input[type=radio] { width: 18px; height: 18px; accent-color: var(--cable); margin: 0; }
.chip { display: inline-flex; align-items: center; gap: 6px; min-height: 34px; padding: 0 12px; border-radius: 17px; border: 1px solid var(--line); background: var(--card); font-size: 0.875rem; cursor: pointer; }
.chip[aria-pressed="true"] { background: var(--ink); color: var(--paper); border-color: var(--ink); }
.chip .dot { width: 8px; height: 8px; border-radius: 50%; background: var(--c, var(--cable)); }

/* ==========================================================================
   Layout pieces
   ========================================================================== */
main { padding-bottom: 72px; min-height: 70vh; }
main:focus, main:focus-visible { outline: none; box-shadow: none; }
.page-head { padding: 44px 0 24px; }
.page-head h1 { font-size: clamp(1.75rem, 4vw, 2.5rem); font-weight: 700; letter-spacing: -0.02em; margin-bottom: 8px; }
.page-head p { max-width: 42rem; color: var(--ink-2); margin: 0; }
.panel { background: var(--card); border: 1px solid var(--line); border-radius: var(--r-lg); }
.section { margin-top: 48px; }
.section > h2 { font-size: 1.375rem; font-weight: 600; margin-bottom: 16px; }
.bar { height: 6px; border-radius: 3px; background: var(--sunk); overflow: hidden; }
.bar > i { display: block; height: 100%; width: 0; background: var(--c, var(--cable)); border-radius: 3px; transition: width .3s; }
.badge { display: inline-flex; align-items: center; padding: 3px 9px; border-radius: 12px; font-size: 0.75rem; font-weight: 600; white-space: nowrap; }
.badge.ok { background: var(--ok-soft); color: var(--ok); }
.badge.neutral { background: var(--sunk); color: var(--ink-2); }
.empty { padding: 28px; border: 1px dashed var(--line); border-radius: var(--r-lg); color: var(--ink-2); text-align: center; }

/* ==========================================================================
   Home
   ========================================================================== */
.hero { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1.05fr); gap: 48px; align-items: center; padding: 56px 0 24px; }
.hero h1 { font-size: clamp(2.25rem, 5.6vw, 3.75rem); font-weight: 700; line-height: 1.05; letter-spacing: -0.035em; margin-bottom: 18px; }
.hero .lead { font-size: 1.125rem; color: var(--ink-2); max-width: 32rem; }
.hero .row { margin-top: 26px; }
.try { margin-top: 12px; display: flex; flex-wrap: wrap; gap: 6px; align-items: center; font-size: 0.875rem; color: var(--ink-2); }
.try button { font: 500 0.8125rem var(--mono); padding: 5px 9px; border-radius: 6px; border: 1px solid var(--line); background: var(--card); cursor: pointer; color: var(--ink); }
.try button:hover { border-color: var(--cable); }
@media (max-width: 900px) { .hero { grid-template-columns: minmax(0, 1fr); gap: 28px; padding-top: 36px; } }

.today { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 0 28px; }
.today a { display: grid; grid-template-columns: 1fr auto; gap: 2px 16px; padding: 16px 0; border-top: 1px solid var(--line); text-decoration: none; color: var(--ink); }
.today a:hover .t-title { color: var(--cable-ink); }
.t-kind { grid-column: 1; font-size: 0.8125rem; color: var(--ink-2); }
.t-title { grid-column: 1; font-weight: 600; }
.t-go { grid-column: 2; grid-row: 1 / span 2; align-self: center; color: var(--cable-ink); font-size: 0.875rem; font-weight: 600; }
@media (max-width: 700px) { .today { grid-template-columns: minmax(0, 1fr); } }

.path { display: grid; grid-template-columns: repeat(4, minmax(0, 1fr)); gap: 16px; }
.phase { padding: 18px 18px 8px; border-top: 4px solid var(--c); }
.phase h3 { font-size: 1.0625rem; font-weight: 600; }
.phase .muted { font-size: 0.8125rem; margin: 4px 0 12px; }
.phase .bar { margin-bottom: 10px; }
.phase ol { list-style: none; }
.phase li a { display: flex; gap: 10px; align-items: baseline; padding: 7px 0; border-top: 1px solid var(--line); text-decoration: none; color: var(--ink); font-size: 0.9375rem; }
.phase li a:hover { color: var(--cable-ink); }
.num { flex: none; width: 24px; font: 500 0.8125rem var(--mono); color: var(--ink-2); }
.done-mark { margin-left: auto; color: var(--ok); font-weight: 700; }
@media (max-width: 1000px) { .path { grid-template-columns: repeat(2, minmax(0, 1fr)); } }
@media (max-width: 560px) { .path { grid-template-columns: minmax(0, 1fr); } }

.stats { display: flex; flex-wrap: wrap; gap: 8px 28px; font-size: 0.9375rem; color: var(--ink-2); }
.stats b { color: var(--ink); font-weight: 600; }

/* ==========================================================================
   Terminal
   ========================================================================== */
.term { display: flex; flex-direction: column; background: var(--term-bg); color: var(--term-ink); border-radius: var(--r-lg); overflow: hidden; font: 400 0.875rem/1.5 var(--mono); box-shadow: 0 18px 40px -18px rgb(14 34 51 / .55); }
.term-bar { display: flex; align-items: center; gap: 10px; padding: 9px 14px; background: rgb(255 255 255 / .05); border-bottom: 1px solid rgb(255 255 255 / .07); font-size: 0.75rem; color: var(--term-dim); }
.term-bar .led { width: 8px; height: 8px; border-radius: 50%; background: #47D17F; box-shadow: 0 0 6px #47D17F; }
.term-bar .grow { flex: 1; }
.term-bar button { background: none; border: 0; color: var(--term-dim); font: inherit; cursor: pointer; padding: 2px 6px; border-radius: 4px; }
.term-bar button:hover { color: var(--term-ink); background: rgb(255 255 255 / .08); }
.term-body { flex: 1; overflow: auto; padding: 12px 14px 14px; cursor: text; min-height: 0; }
.term-out { white-space: pre; margin: 0; font: inherit; }
.term-out .p { color: var(--term-prompt); }
.term-out .e { color: var(--term-err); }
.term-out .s { color: var(--term-sys); }
.term-out .d { color: var(--term-dim); }
.term-line { display: flex; align-items: baseline; }
.term-line .p { color: var(--term-prompt); white-space: pre; }
.term-line input:focus-visible { box-shadow: none; }
.term-line input { flex: 1; min-width: 0; background: transparent; border: 0; outline: none; color: var(--term-ink); font: inherit; padding: 0; caret-color: var(--term-prompt); }
.term:focus-within { box-shadow: 0 18px 40px -18px rgb(14 34 51 / .55), 0 0 0 2px var(--cable); }
.term-hero { height: 360px; font-size: 0.78rem; }
.term-lab { height: min(70vh, 640px); }
@media (max-width: 640px) { .term { font-size: 0.8125rem; } .term-hero { height: 300px; } .term-lab { height: 60vh; } }

/* ==========================================================================
   Lessons
   ========================================================================== */
.lesson-layout { display: grid; grid-template-columns: 250px minmax(0, 1fr); gap: 48px; padding-top: 32px; }
.toc { position: sticky; top: 88px; align-self: start; max-height: calc(100vh - 110px); overflow-y: auto; font-size: 0.875rem; }
.toc h2 { font-size: 0.8125rem; font-weight: 600; color: var(--ink-2); margin: 16px 0 6px; }
.toc h2:first-child { margin-top: 0; }
.toc ol { list-style: none; }
.toc a { display: flex; gap: 8px; padding: 5px 8px; border-radius: 6px; text-decoration: none; color: var(--ink-2); }
.toc a:hover { color: var(--ink); background: var(--sunk); }
.toc a[aria-current="page"] { color: var(--ink); background: var(--card); box-shadow: inset 3px 0 0 var(--c); }
.toc .num { width: 20px; }
@media (max-width: 900px) { .lesson-layout { grid-template-columns: minmax(0, 1fr); gap: 0; } .toc { display: none; } }

.lesson { max-width: 46rem; }
.lesson-meta { display: flex; flex-wrap: wrap; gap: 8px 16px; align-items: center; font-size: 0.875rem; color: var(--ink-2); margin-bottom: 12px; }
.lesson-meta .phase-name { display: inline-flex; align-items: center; gap: 8px; color: var(--c); font-weight: 600; }
.lesson-meta .phase-name::before { content: ''; width: 18px; height: 4px; border-radius: 2px; background: var(--c); }
.lesson h1 { font-size: clamp(1.75rem, 4.2vw, 2.5rem); font-weight: 700; letter-spacing: -0.025em; }
.lesson .en { font-size: 1rem; color: var(--ink-2); margin: 6px 0 22px; }
.lesson .intro { font-size: 1.125rem; line-height: 1.6; margin-bottom: 28px; }
.lesson h2 { font-size: 1.1875rem; font-weight: 600; margin: 34px 0 12px; }
.lesson p, .lesson li { font-size: 1.0rem; }
.lesson ul, .lesson ol { padding-left: 1.3em; margin-bottom: 1em; }
.lesson li { margin: 4px 0; }
.lesson li::marker { color: var(--c); }
.lesson code { background: var(--sunk); padding: 1px 5px; border-radius: 4px; }
.lesson pre { margin: 0 0 18px; padding: 14px 16px; background: var(--term-bg); color: var(--term-ink); border-radius: var(--r); overflow-x: auto; font-size: 0.8125rem; line-height: 1.6; }
.callout { display: flex; gap: 12px; padding: 14px 16px; border-radius: var(--r); margin: 0 0 18px; font-size: 0.9375rem; }
.callout b:first-child { flex: none; }
.callout.note { background: var(--warn-soft); color: var(--warn-ink); }
.callout.tip { background: var(--cable-soft); color: var(--ink); }
.callout code { background: rgb(0 0 0 / .06); }
.table-wrap { overflow-x: auto; margin: 0 0 18px; border: 1px solid var(--line); border-radius: var(--r); background: var(--card); }
table { width: 100%; border-collapse: collapse; font-size: 0.875rem; }
th, td { text-align: left; padding: 9px 12px; border-bottom: 1px solid var(--line); vertical-align: top; }
th { font-weight: 600; background: var(--sunk); color: var(--ink-2); font-size: 0.8125rem; }
tr:last-child td { border-bottom: 0; }
.lesson-foot { display: flex; flex-wrap: wrap; gap: 10px; align-items: center; margin-top: 36px; padding-top: 22px; border-top: 1px solid var(--line); }
.pager { display: flex; justify-content: space-between; gap: 16px; margin-top: 28px; }
.pager a { display: flex; flex-direction: column; gap: 2px; padding: 12px 16px; border: 1px solid var(--line); border-radius: var(--r); text-decoration: none; color: var(--ink); max-width: 48%; background: var(--card); }
.pager a:hover { border-color: var(--cable); }
.pager small { color: var(--ink-2); }
.pager .next { margin-left: auto; text-align: right; }

/* ==========================================================================
   Quiz
   ========================================================================== */
.setup { padding: 22px; display: grid; gap: 22px; max-width: 760px; }
.setup h2 { font-size: 1rem; font-weight: 600; margin-bottom: 10px; }
.topic-grid { display: flex; flex-wrap: wrap; gap: 6px; }
.quiz-card { max-width: 760px; padding: 26px; }
.quiz-top { display: flex; justify-content: space-between; align-items: center; gap: 12px; font-size: 0.875rem; color: var(--ink-2); margin-bottom: 10px; }
.quiz-card .bar { margin-bottom: 22px; }
.quiz-q { font-size: 1.25rem; font-weight: 600; line-height: 1.4; margin-bottom: 20px; }
.options { display: grid; gap: 10px; list-style: none; }
.opt { display: flex; gap: 14px; align-items: flex-start; width: 100%; text-align: left; padding: 13px 16px; border-radius: var(--r); border: 1px solid var(--line); background: var(--card); cursor: pointer; font-size: 1rem; line-height: 1.45; }
.opt:hover:not([disabled]) { border-color: var(--cable); }
.opt kbd { flex: none; display: grid; place-items: center; width: 24px; height: 24px; border-radius: 6px; background: var(--sunk); font-size: 0.75rem; color: var(--ink-2); }
.opt[disabled] { cursor: default; }
.opt.right { border-color: var(--ok); background: var(--ok-soft); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.explain { margin-top: 18px; padding: 14px 16px; border-radius: var(--r); background: var(--sunk); font-size: 0.9375rem; }
.explain b { display: block; margin-bottom: 4px; }
.explain.right b { color: var(--ok); }
.explain.wrong b { color: var(--bad); }
.result-score { font-size: 3rem; font-weight: 700; letter-spacing: -0.03em; line-height: 1; }
.review { list-style: none; margin-top: 20px; }
.review li { padding: 14px 0; border-top: 1px solid var(--line); }
.review .q { font-weight: 600; }
.review .a { color: var(--ok); font-size: 0.9375rem; margin-top: 4px; }

/* ==========================================================================
   Subnet drills
   ========================================================================== */
.drill { display: grid; grid-template-columns: minmax(0, 1.4fr) minmax(0, 1fr); gap: 24px; align-items: start; }
@media (max-width: 900px) { .drill { grid-template-columns: minmax(0, 1fr); } }
.drill-card { padding: 26px; }
.drill-kind { font-size: 0.8125rem; color: var(--ink-2); margin-bottom: 8px; }
.drill-q { font-size: 1.375rem; font-weight: 600; line-height: 1.35; margin-bottom: 20px; }
.drill-q .mono { font-size: 0.95em; color: var(--cable-ink); }
.answer-row { display: flex; gap: 10px; }
.answer-row input { flex: 1; min-width: 0; font-family: var(--mono); font-size: 1.0625rem; }
.feedback { margin-top: 18px; }
.steps { margin: 12px 0 0; padding-left: 1.3em; font-size: 0.9375rem; }
.steps li { margin: 5px 0; }
.steps code { background: rgb(0 0 0 / .06); padding: 0 4px; border-radius: 4px; }
.side { padding: 20px; display: grid; gap: 18px; }
.side h2 { font-size: 0.9375rem; font-weight: 600; margin-bottom: 8px; }
.kinds { display: grid; gap: 6px; }
.score-line { display: flex; gap: 22px; font-size: 0.9375rem; color: var(--ink-2); }
.score-line b { color: var(--ink); font-size: 1.25rem; display: block; }

/* ==========================================================================
   Labs
   ========================================================================== */
.lab-list { list-style: none; }
.lab-row { display: grid; grid-template-columns: 6px minmax(0, 1fr) auto; gap: 16px; align-items: center; padding: 16px 0; border-top: 1px solid var(--line); text-decoration: none; color: var(--ink); }
.lab-row:hover .lab-title { color: var(--cable-ink); }
.lab-row .stripe { align-self: stretch; border-radius: 3px; background: var(--c); }
.lab-title { font-weight: 600; }
.lab-sub { font-size: 0.875rem; color: var(--ink-2); }
.lab-layout { display: grid; grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.25fr); gap: 24px; align-items: start; padding-top: 24px; }
@media (max-width: 1000px) { .lab-layout { grid-template-columns: minmax(0, 1fr); } }
.brief { padding: 22px; }
.brief h1 { font-size: 1.5rem; font-weight: 700; margin: 4px 0 10px; }
.brief pre { margin: 14px 0 0; padding: 12px 14px; background: var(--sunk); border-radius: var(--r); font-size: 0.75rem; line-height: 1.55; overflow-x: auto; }
.tasks { list-style: none; margin-top: 18px; counter-reset: task; }
.task { display: grid; grid-template-columns: 26px minmax(0, 1fr); gap: 4px 10px; padding: 12px 0; border-top: 1px solid var(--line); }
.task .box { width: 22px; height: 22px; border-radius: 6px; border: 2px solid var(--line); display: grid; place-items: center; margin-top: 1px; transition: background-color .2s, border-color .2s; }
.task.done .box { background: var(--ok); border-color: var(--ok); }
.task.done .box::after { content: ''; width: 6px; height: 11px; border: solid #fff; border-width: 0 2px 2px 0; transform: translateY(-1px) rotate(45deg); }
.task.done .ttext { color: var(--ink-2); }
.task .hint-btn { grid-column: 2; justify-self: start; background: none; border: 0; padding: 0; color: var(--cable-ink); font-size: 0.8125rem; cursor: pointer; text-decoration: underline; text-underline-offset: 3px; }
.task pre { grid-column: 2; margin: 6px 0 0; padding: 8px 10px; background: var(--term-bg); color: var(--term-ink); border-radius: 6px; font-size: 0.8125rem; }
.lab-done { margin-top: 16px; padding: 14px 16px; border-radius: var(--r); background: var(--ok-soft); color: var(--ok); font-weight: 600; }
.cheat { margin-top: 12px; font-size: 0.8125rem; color: var(--ink-2); }
.cheat kbd { font-size: 0.75rem; padding: 1px 5px; border-radius: 4px; border: 1px solid var(--line); background: var(--card); }

/* ==========================================================================
   Flashcards
   ========================================================================== */
.cards-wrap { max-width: 680px; }
.flash { display: block; position: relative; width: 100%; min-height: 280px; perspective: 1400px; cursor: pointer; border: 0; background: none; padding: 0; text-align: left; }
.flash-inner { display: block; position: relative; width: 100%; min-height: 280px; transition: transform .45s cubic-bezier(.3, .7, .2, 1); transform-style: preserve-3d; }
.flash[aria-pressed="true"] .flash-inner { transform: rotateY(180deg); }
.face { position: absolute; inset: 0; display: flex; flex-direction: column; justify-content: center; gap: 10px; padding: 32px; border-radius: var(--r-lg); background: var(--card); border: 1px solid var(--line); backface-visibility: hidden; -webkit-backface-visibility: hidden; border-top: 4px solid var(--c); }
.face.back { transform: rotateY(180deg); }
.face small { color: var(--ink-2); font-size: 0.8125rem; }
.face .front-text { font-size: 1.625rem; font-weight: 600; line-height: 1.3; }
.face .back-text { font-size: 1.125rem; line-height: 1.55; white-space: pre-line; }
.card-actions { display: flex; gap: 10px; margin-top: 16px; }
.card-actions .btn { flex: 1; }

/* ==========================================================================
   Footer, toast, motion
   ========================================================================== */
.foot { border-top: 1px solid var(--line); padding: 24px 0 36px; font-size: 0.875rem; color: var(--ink-2); }
.foot .wrap { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 10px 24px; }
.foot button { background: none; border: 0; padding: 0; color: var(--cable-ink); cursor: pointer; text-decoration: underline; text-underline-offset: 3px; }
.toast { position: fixed; left: 50%; bottom: 22px; transform: translateX(-50%); z-index: 60; background: var(--ink); color: var(--paper); padding: 10px 18px; border-radius: var(--r); font-size: 0.9375rem; box-shadow: 0 10px 30px rgb(0 0 0 / .2); }
@media (prefers-reduced-motion: reduce) { *, *::before, *::after { transition: none !important; animation: none !important; } }
.stats-gap { margin-top: 16px; }

.btn kbd { font: 500 0.75rem var(--mono); opacity: .7; }
.lesson pre code { background: none; padding: 0; color: inherit; font-size: inherit; }