/* =========================================================
   Subnet// — design tokens
   ========================================================= */
:root{
  --bg:            #0A0E12;
  --bg-elevated:   #10151C;
  --bg-inset:      #0D1218;
  --border:        #1C2530;
  --border-soft:   #161D26;
  --text:          #E8EDF1;
  --text-dim:      #7C8B9C;
  --text-faint:    #4B5866;

  --net:           #00E5C7;   /* network bits / calculator mode  */
  --net-dim:       #0A5F55;
  --host:          #FFB238;   /* host bits                       */
  --host-dim:      #6B4A14;
  --quiz:          #A78BFA;   /* practice mode accent            */
  --quiz-dim:      #4B3E80;
  --danger:        #FF5D5D;
  --success:       #4ADE80;

  --font-mono: 'JetBrains Mono', 'Vazirmatn', ui-monospace, monospace;
  --font-body: 'Inter', 'Vazirmatn', -apple-system, sans-serif;
  --font-fa:   'Vazirmatn', 'JetBrains Mono', sans-serif;

  --radius: 6px;
  --container: 900px;
}

html[lang="fa"]{
  --font-body: 'Vazirmatn', sans-serif;
}

*,*::before,*::after{ box-sizing:border-box; }
html{ scroll-behavior:smooth; }

body{
  margin:0;
  background:
    radial-gradient(ellipse 900px 500px at 50% -10%, rgba(0,229,199,0.07), transparent 60%),
    var(--bg);
  color:var(--text);
  font-family:var(--font-body);
  line-height:1.5;
  -webkit-font-smoothing:antialiased;
  min-height:100vh;
}

html[dir="rtl"] body{ font-family:var(--font-fa); }

/* subtle CRT scanline atmosphere, decorative only */
.scanline-overlay{
  position:fixed; inset:0; pointer-events:none; z-index:1;
  background:repeating-linear-gradient(
    to bottom, rgba(255,255,255,0.012) 0px, rgba(255,255,255,0.012) 1px,
    transparent 1px, transparent 3px
  );
  mix-blend-mode:overlay;
}

a{ color:inherit; }

/* =========================================================
   Header
   ========================================================= */
.site-header{
  position:sticky; top:0; z-index:20;
  background:rgba(10,14,18,0.85);
  backdrop-filter:blur(10px);
  border-bottom:1px solid var(--border-soft);
}
.header-inner{
  max-width:var(--container); margin:0 auto;
  padding:16px 20px;
  display:flex; align-items:center; justify-content:space-between;
}
.brand{
  font-family:var(--font-mono);
  font-weight:700; font-size:18px;
  text-decoration:none; color:var(--text);
  display:inline-flex; align-items:baseline; gap:2px;
  letter-spacing:-0.02em;
}
.brand-slash{ color:var(--net); }
.brand-cursor{
  color:var(--net); margin-inline-start:2px;
  animation:blink 1.1s steps(1) infinite;
}
@keyframes blink{ 50%{ opacity:0; } }

.lang-toggle{
  font-family:var(--font-mono); font-size:13px; font-weight:600;
  background:var(--bg-elevated); border:1px solid var(--border);
  border-radius:999px; padding:6px 12px; cursor:pointer;
  color:var(--text-dim); display:inline-flex; align-items:center; gap:6px;
  transition:border-color .15s ease;
}
.lang-toggle:hover{ border-color:var(--net-dim); }
.lang-toggle .lang-sep{ color:var(--text-faint); }
.lang-toggle .active{ color:var(--net); }

/* =========================================================
   Layout
   ========================================================= */
main{ max-width:var(--container); margin:0 auto; padding:0 20px 80px; position:relative; z-index:2; }

.hero{ padding:56px 0 40px; text-align:center; }
.eyebrow{
  font-family:var(--font-mono); font-size:13px; color:var(--net);
  letter-spacing:0.02em; margin:0 0 14px;
}
.hero h1{
  font-family:var(--font-mono); font-weight:800;
  font-size:clamp(32px,5.5vw,52px); line-height:1.08;
  margin:0 0 18px; letter-spacing:-0.02em;
}
html[dir="rtl"] .hero h1{ font-family:var(--font-fa); }
.hero-sub{
  color:var(--text-dim); font-size:16px; max-width:560px; margin:0 auto;
}

/* Mode tabs */
.mode-tabs{
  display:flex; gap:8px; justify-content:center;
  margin:0 0 32px; border-bottom:1px solid var(--border-soft);
}
.mode-tab{
  font-family:var(--font-mono); font-size:14px; font-weight:600;
  background:none; border:none; color:var(--text-dim);
  padding:12px 18px; cursor:pointer; position:relative;
  border-bottom:2px solid transparent; margin-bottom:-1px;
  transition:color .15s ease;
}
html[dir="rtl"] .mode-tab{ font-family:var(--font-fa); }
.mode-tab:hover{ color:var(--text); }
.mode-tab.active{ color:var(--net); border-bottom-color:var(--net); }
#tabQuiz.active{ color:var(--quiz); border-bottom-color:var(--quiz); }

.panel.hidden{ display:none; }

/* =========================================================
   Cards
   ========================================================= */
.card{
  background:var(--bg-elevated);
  border:1px solid var(--border);
  border-radius:var(--radius);
  padding:22px;
}
.field-label{
  font-family:var(--font-mono); font-size:12px; text-transform:uppercase;
  letter-spacing:0.06em; color:var(--text-faint); margin:0 0 10px;
  display:block;
}
html[dir="rtl"] .field-label{ font-family:var(--font-fa); text-transform:none; }

/* =========================================================
   Calculator
   ========================================================= */
.calc-grid{
  display:grid; grid-template-columns:1fr 1fr; gap:16px; margin-bottom:16px;
}
@media (max-width:720px){ .calc-grid{ grid-template-columns:1fr; } }

.ip-input{
  width:100%; font-family:var(--font-mono); font-size:22px; font-weight:600;
  background:var(--bg-inset); border:1px solid var(--border);
  border-radius:var(--radius); color:var(--net); padding:12px 14px;
  letter-spacing:0.02em; margin-bottom:20px;
}
.ip-input:focus{ outline:2px solid var(--net); outline-offset:1px; border-color:transparent; }
.ip-input.invalid{ color:var(--danger); }

.cidr-row{ display:flex; align-items:baseline; justify-content:space-between; margin-bottom:6px; }
.cidr-row .field-label{ margin:0; }
.cidr-value{ font-family:var(--font-mono); font-size:18px; font-weight:700; color:var(--host); }

.cidr-slider{
  width:100%; appearance:none; height:4px; border-radius:2px;
  background:linear-gradient(to right, var(--net) 0%, var(--net) var(--fill,75%), var(--border) var(--fill,75%), var(--border) 100%);
  margin:10px 0 16px; cursor:pointer;
}
.cidr-slider::-webkit-slider-thumb{
  appearance:none; width:16px; height:16px; border-radius:50%;
  background:var(--host); border:2px solid var(--bg); cursor:pointer;
  box-shadow:0 0 0 1px var(--host);
}
.cidr-slider::-moz-range-thumb{
  width:16px; height:16px; border-radius:50%; border:2px solid var(--bg);
  background:var(--host); cursor:pointer; box-shadow:0 0 0 1px var(--host);
}
/* In RTL, the track should fill from the right, matching the thumb's
   right-to-left travel direction and the page's reading direction. */
html[dir="rtl"] .cidr-slider{
  direction:rtl;
  background:linear-gradient(to left, var(--net) 0%, var(--net) var(--fill,75%), var(--border) var(--fill,75%), var(--border) 100%);
}

.quick-cidrs{ display:flex; flex-wrap:wrap; gap:6px; }
.quick-cidrs button{
  font-family:var(--font-mono); font-size:12px; font-weight:600;
  background:var(--bg-inset); border:1px solid var(--border); color:var(--text-dim);
  border-radius:4px; padding:5px 9px; cursor:pointer; transition:all .12s ease;
}
.quick-cidrs button:hover{ border-color:var(--net); color:var(--net); }

.input-error{
  min-height:18px; color:var(--danger); font-size:13px; margin:8px 0 0;
  font-family:var(--font-mono);
}

/* Bit grid — the signature element */
.bitgrid-card{ display:flex; flex-direction:column; }
.bitgrid{
  display:grid; grid-template-columns:repeat(8,1fr); gap:4px;
  margin-bottom:14px;
}
.bit{
  aspect-ratio:1; border-radius:3px; background:var(--bg-inset);
  border:1px solid var(--border);
  display:flex; align-items:center; justify-content:center;
  font-family:var(--font-mono); font-size:11px; font-weight:600;
  color:var(--text-faint); transition:background .12s ease, color .12s ease, border-color .12s ease;
}
.bit.net{ background:var(--net-dim); border-color:var(--net); color:var(--net); }
.bit.host{ background:var(--host-dim); border-color:var(--host); color:var(--host); }
.octet-gap{ grid-column:span 8; height:2px; }

.bitgrid-legend{ display:flex; gap:18px; margin-top:auto; }
.legend-item{ display:flex; align-items:center; gap:6px; font-size:12px; color:var(--text-dim); font-family:var(--font-mono); }
html[dir="rtl"] .legend-item{ font-family:var(--font-fa); }
.swatch{ width:10px; height:10px; border-radius:2px; display:inline-block; }
.swatch-net{ background:var(--net); }
.swatch-host{ background:var(--host); }

/* Results grid */
.results-grid{
  display:grid; grid-template-columns:repeat(3,1fr); gap:12px; margin-bottom:16px;
}
@media (max-width:720px){ .results-grid{ grid-template-columns:repeat(2,1fr); } }
@media (max-width:460px){ .results-grid{ grid-template-columns:1fr; } }

.result-cell{
  background:var(--bg-elevated); border:1px solid var(--border); border-radius:var(--radius);
  padding:14px 16px;
}
.result-cell .rl{
  font-family:var(--font-mono); font-size:11px; text-transform:uppercase; letter-spacing:0.05em;
  color:var(--text-faint); margin:0 0 6px;
}
html[dir="rtl"] .result-cell .rl{ font-family:var(--font-fa); text-transform:none; }
.result-cell .rv{
  font-family:var(--font-mono); font-size:17px; font-weight:700; color:var(--text);
  word-break:break-all;
}

/* Host range: three stacked lines (first IP / connector word / last IP)
   instead of one long dashed line that wraps awkwardly. */
.range-value{
  display:flex; flex-direction:column; gap:1px;
  font-family:var(--font-mono); font-weight:700; color:var(--text);
}
.range-value .range-ip{ font-size:16px; }
.range-value .range-sep{
  font-size:11px; font-weight:600; color:var(--text-faint);
  text-transform:uppercase; letter-spacing:0.05em; margin:1px 0;
}
html[dir="rtl"] .range-value .range-sep{ font-family:var(--font-fa); text-transform:none; }

.explainer-text{ color:var(--text-dim); font-size:14px; margin:0; line-height:1.6; }

/* =========================================================
   Quiz
   ========================================================= */
.quiz-toolbar{
  display:flex; align-items:center; justify-content:space-between; flex-wrap:wrap;
  gap:16px; margin-bottom:16px;
}
.difficulty-group{ display:flex; gap:6px; }
.diff-btn{
  font-family:var(--font-mono); font-size:13px; font-weight:600;
  background:var(--bg-inset); border:1px solid var(--border); color:var(--text-dim);
  border-radius:4px; padding:7px 14px; cursor:pointer;
}
html[dir="rtl"] .diff-btn{ font-family:var(--font-fa); }
.diff-btn.active{ border-color:var(--quiz); color:var(--quiz); background:rgba(167,139,250,0.08); }

.quiz-stats{ display:flex; gap:22px; }
.stat{ text-align:center; }
.stat-value{ display:block; font-family:var(--font-mono); font-size:20px; font-weight:800; color:var(--quiz); }
.stat-label{ font-family:var(--font-mono); font-size:10px; text-transform:uppercase; color:var(--text-faint); letter-spacing:0.05em; }
html[dir="rtl"] .stat-label{ font-family:var(--font-fa); text-transform:none; }

.quiz-card{ text-align:center; padding:36px 24px; }
.quiz-eyebrow{
  font-family:var(--font-mono); font-size:13px; color:var(--text-faint); margin:0 0 10px;
}
.quiz-question{ font-size:20px; font-weight:600; margin:0 0 26px; line-height:1.5; }

.quiz-answer-row{ display:flex; gap:10px; max-width:380px; margin:0 auto; }
.quiz-input{
  flex:1; font-family:var(--font-mono); font-size:16px; font-weight:600;
  background:var(--bg-inset); border:1px solid var(--border); border-radius:var(--radius);
  color:var(--text); padding:12px 14px; text-align:center;
}
.quiz-input:focus{ outline:2px solid var(--quiz); outline-offset:1px; border-color:transparent; }

.btn-primary{
  font-family:var(--font-mono); font-weight:700; font-size:14px;
  background:var(--quiz); color:#160E2B; border:none; border-radius:var(--radius);
  padding:0 20px; cursor:pointer; transition:filter .12s ease;
}
.btn-primary:hover{ filter:brightness(1.1); }

.quiz-feedback{
  min-height:24px; margin:18px 0 4px; font-family:var(--font-mono); font-weight:600; font-size:14px;
}
.quiz-feedback.correct{ color:var(--success); }
.quiz-feedback.wrong{ color:var(--danger); }

.btn-ghost{
  margin-top:14px; background:none; border:none; color:var(--text-dim);
  font-family:var(--font-mono); font-size:13px; cursor:pointer; text-decoration:underline;
  text-underline-offset:3px;
}
html[dir="rtl"] .btn-ghost, html[dir="rtl"] .btn-primary, html[dir="rtl"] .quiz-input{ font-family:var(--font-fa); }
.btn-ghost:hover{ color:var(--text); }
.btn-ghost.hidden{ visibility:hidden; }

/* =========================================================
   Footer
   ========================================================= */
.site-footer{
  text-align:center; padding:30px 20px 50px; color:var(--text-faint);
  font-family:var(--font-mono); font-size:12px; position:relative; z-index:2;
}
.site-footer p{ margin:0 0 8px; }
.site-footer p:last-child{ margin-bottom:0; }
html[dir="rtl"] .site-footer{ font-family:var(--font-fa); }

.footer-credit{
  font-size:12px; letter-spacing:0.02em;
}
.footer-credit a{
  color:var(--net); text-decoration:none; font-weight:700;
  border-bottom:1px solid var(--net-dim);
  transition:border-color .15s ease, color .15s ease;
}
.footer-credit a:hover{ border-color:var(--net); color:var(--text); }

/* Focus visibility for a11y */
button:focus-visible, input:focus-visible{
  outline:2px solid var(--net); outline-offset:2px;
}

@media (prefers-reduced-motion:reduce){
  .brand-cursor{ animation:none; }
  html{ scroll-behavior:auto; }
}