/* ==========================================================================
   Burhan Aviation Technical Consultancy
   Design system — "technical & precise"
   Single stylesheet, no dependencies.
   ========================================================================== */

:root{
  /* Ink / surfaces */
  --ink:        #0B1116;   /* near-black, cool */
  --ink-2:      #131C24;   /* raised dark panel */
  --ink-3:      #1D2831;   /* dark hairline */
  --paper:      #F5F7F8;   /* page ground */
  --paper-2:    #FFFFFF;   /* cards */
  --paper-3:    #ECF0F2;   /* muted band */

  /* Type */
  --text:       #16202A;
  --text-2:     #55636E;
  --text-inv:   #EEF3F6;
  --text-inv-2: #9BAAB6;

  /* Lines */
  --rule:       #DCE3E7;
  --rule-dark:  rgba(255,255,255,.13);

  /* Signal */
  --amber:      #E39A11;
  --amber-soft: #FBEED2;
  --steel:      #2E6C8E;

  /* Metrics */
  --measure: 68ch;
  --gap: clamp(1rem, 2.2vw, 1.75rem);
  --pad-x: clamp(1.15rem, 5vw, 4.5rem);
  --sec-y: clamp(3.5rem, 8vw, 7rem);

  --sans:    "IBM Plex Sans", ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --display: "Archivo", "IBM Plex Sans", ui-sans-serif, system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --mono:    "IBM Plex Mono", ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
}

*,*::before,*::after{ box-sizing:border-box; }

html{ -webkit-text-size-adjust:100%; scroll-behavior:smooth; }

body{
  margin:0;
  background:var(--paper);
  color:var(--text);
  font-family:var(--sans);
  font-size:clamp(1rem, .96rem + .18vw, 1.075rem);
  line-height:1.65;
  -webkit-font-smoothing:antialiased;
}

img{ max-width:100%; display:block; }

a{ color:inherit; }

h1,h2,h3,h4{
  margin:0;
  font-family:var(--display);
  line-height:1.12;
  letter-spacing:-.022em;
  font-weight:600;
  text-wrap:balance;
}
h1{ font-size:clamp(2.15rem, 1.35rem + 3.4vw, 4rem); }
h2{ font-size:clamp(1.6rem, 1.15rem + 1.9vw, 2.5rem); }
h3{ font-size:clamp(1.1rem, 1rem + .5vw, 1.35rem); letter-spacing:-.012em; }

p{ margin:0 0 1.05em; max-width:var(--measure); }
p:last-child{ margin-bottom:0; }

/* --- Layout ---------------------------------------------------------- */

.wrap{ max-width:1220px; margin-inline:auto; padding-inline:var(--pad-x); }
.section{ padding-block:var(--sec-y); }
.section--tight{ padding-block:clamp(2.5rem,5vw,4rem); }

.dark{ background:var(--ink); color:var(--text-inv); }
.dark p{ color:var(--text-inv-2); }
.dark h1,.dark h2,.dark h3{ color:var(--text-inv); }

/* --- Small caps label ------------------------------------------------ */

.label{
  font-family:var(--mono);
  font-size:.7rem;
  letter-spacing:.16em;
  text-transform:uppercase;
  color:var(--text-2);
  display:flex;
  align-items:center;
  gap:.7rem;
  margin:0 0 1.4rem;
  font-weight:500;
}
.label::before{
  content:"";
  width:1.6rem; height:1px;
  background:var(--amber);
  flex:none;
}
.dark .label{ color:var(--text-inv-2); }

/* --- Header ---------------------------------------------------------- */

.site-head{
  position:sticky; top:0; z-index:60;
  background:rgba(11,17,22,.94);
  backdrop-filter:saturate(150%) blur(10px);
  border-bottom:1px solid var(--rule-dark);
  color:var(--text-inv);
}
.site-head__inner{
  display:flex; align-items:center; justify-content:space-between;
  gap:1rem;
  min-height:70px;
}
.brand{
  display:flex; align-items:center; gap:.75rem;
  text-decoration:none; color:var(--text-inv);
  padding-block:.6rem;
}
.brand__mark{ width:30px; height:30px; flex:none; }
.brand__txt{ display:flex; flex-direction:column; line-height:1.12; }
/* BATC logotype: a four-letter mark, so it is set larger and tracked out */
.brand__name{
  font-family:var(--display); font-weight:700;
  letter-spacing:.04em; font-size:1.28rem; line-height:1;
}
.brand__sub{
  font-family:var(--mono); font-size:.58rem; letter-spacing:.11em;
  text-transform:uppercase; color:var(--text-inv-2); margin-top:.25rem;
}
/* on the narrowest phones the descriptor is dropped, the mark carries it */
@media (max-width:400px){ .brand__sub{ display:none; } }

.nav{ display:flex; align-items:center; gap:.15rem; }
.nav a{
  text-decoration:none;
  font-size:.9rem;
  color:var(--text-inv-2);
  padding:.55rem .85rem;
  border-radius:3px;
  transition:color .15s, background .15s;
}
.nav a:hover{ color:var(--text-inv); background:rgba(255,255,255,.06); }
.nav a[aria-current="page"]{ color:var(--text-inv); }
.nav a[aria-current="page"]::after{
  content:""; display:block; height:1px; background:var(--amber);
  margin-top:.3rem;
}
.nav .btn{ margin-left:.6rem; }
/* the .nav a colour rule must not win over the button's own colour */
.nav a.btn--primary{ color:#1B1403; }
.nav a.btn--primary:hover{ color:#1B1403; background:#F2A916; }
.nav a.btn--ghost{ color:var(--text-inv); }

.nav-toggle{
  display:none;
  background:none; border:1px solid var(--rule-dark);
  color:var(--text-inv);
  border-radius:3px; padding:.5rem .75rem;
  font-family:var(--mono); font-size:.72rem; letter-spacing:.12em;
  text-transform:uppercase; cursor:pointer;
}

@media (max-width:860px){
  .nav-toggle{ display:block; }
  .nav{
    position:absolute; inset:70px 0 auto 0;
    flex-direction:column; align-items:stretch;
    background:var(--ink);
    border-bottom:1px solid var(--rule-dark);
    padding:.6rem var(--pad-x) 1.4rem;
    gap:0;
  }
  .nav[hidden]{ display:none; }
  .nav a{ padding:.85rem 0; border-bottom:1px solid var(--rule-dark); border-radius:0; }
  .nav a[aria-current="page"]::after{ display:none; }
  .nav .btn{ margin:1rem 0 0; justify-content:center; border-bottom:0; }
}

/* --- Buttons --------------------------------------------------------- */

.btn{
  display:inline-flex; align-items:center; gap:.55rem;
  font-size:.9rem; font-weight:560;
  padding:.72rem 1.25rem;
  border-radius:3px;
  text-decoration:none;
  border:1px solid transparent;
  cursor:pointer;
  transition:background .16s, border-color .16s, color .16s, transform .16s;
  font-family:inherit;
}
.btn:active{ transform:translateY(1px); }
.btn--primary{ background:var(--amber); color:#1B1403; border-color:var(--amber); }
.btn--primary:hover{ background:#F2A916; border-color:#F2A916; }
.btn--ghost{ border-color:var(--rule-dark); color:var(--text-inv); }
.btn--ghost:hover{ background:rgba(255,255,255,.08); }
.btn--outline{ border-color:var(--text); color:var(--text); }
.btn--outline:hover{ background:var(--ink); color:var(--text-inv); border-color:var(--ink); }
.btn__arrow{ font-family:var(--mono); }

/* --- Hero ------------------------------------------------------------ */

.hero{
  position:relative;
  background:var(--ink);
  color:var(--text-inv);
  overflow:hidden;
  border-bottom:1px solid var(--rule-dark);
}
.hero__grid{
  position:absolute; inset:0;
  background-image:
    linear-gradient(rgba(255,255,255,.045) 1px, transparent 1px),
    linear-gradient(90deg, rgba(255,255,255,.045) 1px, transparent 1px);
  background-size:64px 64px;
  mask-image:radial-gradient(120% 90% at 78% 15%, #000 0%, transparent 72%);
  pointer-events:none;
}
.hero__glow{
  position:absolute; right:-12%; top:-30%;
  width:min(760px,80vw); aspect-ratio:1;
  background:radial-gradient(circle, rgba(227,154,17,.16), transparent 62%);
  pointer-events:none;
}
.hero__inner{
  position:relative;
  padding-block:clamp(4rem,11vw,8.5rem) clamp(3rem,7vw,5.5rem);
}
.hero h1{ max-width:17ch; }
.hero__lede{
  margin-top:1.6rem;
  font-size:clamp(1.05rem,.98rem + .5vw,1.3rem);
  color:var(--text-inv-2);
  max-width:56ch;
  line-height:1.6;
}
.hero__cta{ display:flex; flex-wrap:wrap; gap:.75rem; margin-top:2.4rem; }

.hero__strip{
  position:relative;
  border-top:1px solid var(--rule-dark);
  display:grid;
  grid-template-columns:repeat(4,1fr);
}
.hero__strip div{
  padding:1.5rem var(--pad-x);
  border-left:1px solid var(--rule-dark);
}
.hero__strip div:first-child{ border-left:0; }
.hero__strip dt{
  font-family:var(--mono); font-size:.65rem; letter-spacing:.15em;
  text-transform:uppercase; color:var(--text-inv-2); margin-bottom:.45rem;
}
.hero__strip dd{ margin:0; font-size:.98rem; font-weight:560; letter-spacing:-.01em; }
@media (max-width:860px){
  .hero__strip{ grid-template-columns:repeat(2,1fr); }
  .hero__strip div:nth-child(3){ border-left:0; }
  .hero__strip div:nth-child(n+3){ border-top:1px solid var(--rule-dark); }
}

/* --- Page header (inner pages) --------------------------------------- */

.pagehead{
  background:var(--ink); color:var(--text-inv);
  padding-block:clamp(3rem,7vw,5.5rem) clamp(2.4rem,5vw,4rem);
  position:relative; overflow:hidden;
  border-bottom:1px solid var(--rule-dark);
}
.pagehead .hero__grid{ mask-image:radial-gradient(110% 100% at 85% 0%, #000 0%, transparent 70%); }
.pagehead__inner{ position:relative; }
.pagehead p{ margin-top:1.2rem; color:var(--text-inv-2); font-size:clamp(1rem,.96rem + .35vw,1.18rem); }

/* --- Grids ----------------------------------------------------------- */

.grid{ display:grid; gap:var(--gap); }
.grid--4{ grid-template-columns:repeat(4,1fr); }
.grid--3{ grid-template-columns:repeat(3,1fr); }
.grid--2{ grid-template-columns:repeat(2,1fr); }
.grid--split{ grid-template-columns:minmax(0,.85fr) minmax(0,1.15fr); gap:clamp(2rem,5vw,4.5rem); align-items:start; }
.grid--split-rev{ grid-template-columns:minmax(0,1.15fr) minmax(0,.85fr); }
@media (max-width:1100px){ .grid--4{ grid-template-columns:repeat(2,1fr); } }
@media (max-width:960px){ .grid--3{ grid-template-columns:repeat(2,1fr); } }
@media (max-width:700px){ .grid--4{ grid-template-columns:1fr; } }
@media (max-width:760px){
  .grid--3,.grid--2,.grid--split,.grid--split-rev{ grid-template-columns:1fr; }
}

/* --- Service cards --------------------------------------------------- */

.card{
  background:var(--paper-2);
  border:1px solid var(--rule);
  border-radius:4px;
  padding:clamp(1.35rem,2.4vw,1.9rem);
  display:flex; flex-direction:column; gap:.7rem;
  text-decoration:none; color:inherit;
  transition:border-color .18s, box-shadow .18s, transform .18s;
  position:relative;
}
a.card:hover{
  border-color:var(--ink-3);
  box-shadow:0 12px 32px -20px rgba(11,17,22,.55);
  transform:translateY(-2px);
}
.card__no{
  font-family:var(--mono); font-size:.68rem; letter-spacing:.14em;
  color:var(--amber); font-weight:600;
}
.card p{ color:var(--text-2); font-size:.95rem; margin:0; }
.card__more{
  margin-top:auto; padding-top:.6rem;
  font-family:var(--mono); font-size:.7rem; letter-spacing:.13em;
  text-transform:uppercase; color:var(--text);
}
a.card:hover .card__more{ color:var(--amber); }

/* --- Feature rows (numbered points) ---------------------------------- */

.points{ list-style:none; margin:0; padding:0; }
.points li{
  display:grid;
  grid-template-columns:auto 1fr;
  gap:1.1rem;
  padding:1.35rem 0;
  border-top:1px solid var(--rule);
}
.points li:last-child{ border-bottom:1px solid var(--rule); }
.dark .points li{ border-color:var(--rule-dark); }
.points__no{
  font-family:var(--mono); font-size:.7rem; letter-spacing:.12em;
  color:var(--amber); padding-top:.32rem; font-weight:600;
}
.points h3{ margin-bottom:.35rem; }
.points p{ color:var(--text-2); font-size:.95rem; margin:0; }
.dark .points p{ color:var(--text-inv-2); }

/* --- Detailed service block ------------------------------------------ */

.svc{
  border-top:1px solid var(--rule);
  padding-block:clamp(2.2rem,4.5vw,3.4rem);
  display:grid;
  grid-template-columns:minmax(0,.8fr) minmax(0,1.2fr);
  gap:clamp(1.4rem,4vw,3.5rem);
  scroll-margin-top:90px;
}
@media (max-width:820px){ .svc{ grid-template-columns:1fr; gap:1.2rem; } }
.svc__no{
  font-family:var(--mono); font-size:.7rem; letter-spacing:.14em;
  color:var(--amber); font-weight:600; margin-bottom:.7rem;
}
.svc__lede{ color:var(--text-2); margin-top:.9rem; }
.svc h4{
  font-family:var(--mono); font-size:.7rem; letter-spacing:.14em;
  text-transform:uppercase; color:var(--text-2); font-weight:500;
  margin:0 0 .8rem;
}
.checks{ list-style:none; margin:0 0 1.6rem; padding:0; display:grid; gap:.5rem; }
.checks li{
  position:relative; padding-left:1.5rem;
  font-size:.95rem; color:var(--text-2);
}
.checks li::before{
  content:""; position:absolute; left:0; top:.62em;
  width:.5rem; height:1px; background:var(--amber);
}
.svc__out{
  background:var(--paper-3);
  border-left:2px solid var(--amber);
  padding:1rem 1.2rem;
  font-size:.93rem;
  color:var(--text-2);
}
.svc__out strong{ color:var(--text); font-weight:600; }

/* --- Service group heading ------------------------------------------- */

.svcgroup{
  display:flex; align-items:baseline; gap:1rem;
  padding-top:clamp(2.4rem,5vw,3.6rem);
  padding-bottom:.2rem;
}
.svcgroup:first-child{ padding-top:0; }
.svcgroup__k{
  font-family:var(--mono); font-size:.68rem; letter-spacing:.16em;
  text-transform:uppercase; color:var(--amber); font-weight:600; flex:none;
}
.svcgroup h2{ font-size:clamp(1.25rem,1.1rem + .7vw,1.6rem); }
.svcgroup p{
  font-size:.92rem; color:var(--text-2); margin:0; flex:1 1 22ch; min-width:16ch;
}
@media (max-width:700px){ .svcgroup{ flex-wrap:wrap; gap:.5rem 1rem; } }

/* --- Prose ----------------------------------------------------------- */

.prose h2{ margin-top:2.6rem; margin-bottom:.9rem; }
.prose h2:first-child{ margin-top:0; }
.prose h3{ margin-top:1.9rem; margin-bottom:.5rem; }
.prose ul{ padding-left:1.15rem; color:var(--text-2); max-width:var(--measure); }
.prose li{ margin-bottom:.4rem; }
.lede{ font-size:clamp(1.08rem,1rem + .5vw,1.28rem); color:var(--text-2); line-height:1.6; }

/* --- Aside / spec table ---------------------------------------------- */

.spec{
  border:1px solid var(--rule);
  border-radius:4px;
  background:var(--paper-2);
  padding:1.5rem;
  position:sticky; top:92px;
}
@media (max-width:760px){ .spec{ position:static; } }
.spec dl{ margin:0; }
.spec dt{
  font-family:var(--mono); font-size:.65rem; letter-spacing:.14em;
  text-transform:uppercase; color:var(--text-2);
}
.spec dd{
  margin:.25rem 0 1.1rem; font-size:.95rem; font-weight:520;
  padding-bottom:1.1rem; border-bottom:1px solid var(--rule);
}
.spec dd:last-of-type{ margin-bottom:0; padding-bottom:0; border-bottom:0; }

/* --- Partners -------------------------------------------------------- */

.partners{
  display:grid;
  grid-template-columns:repeat(auto-fit, minmax(215px, 1fr));
  gap:var(--gap);
}
@media (max-width:560px){ .partners{ grid-template-columns:1fr; } }
.partner__where{
  font-family:var(--mono); font-size:.66rem; letter-spacing:.1em;
  color:var(--text-inv); margin-bottom:.55rem;
}
.partner{
  border:1px solid var(--rule-dark);
  border-radius:4px;
  padding:1.4rem 1.5rem;
}
.partner__name{ font-weight:600; letter-spacing:-.01em; margin-bottom:.3rem; }
.partner__meta{
  font-family:var(--mono); font-size:.66rem; letter-spacing:.13em;
  text-transform:uppercase; color:var(--amber); margin-bottom:.6rem;
}
.partner p{ font-size:.92rem; margin:0; }

/* --- Sourced capability panel ---------------------------------------- */
/* Deliberately not styled as one of the numbered disciplines: this work is
   channelled through a named supplier, not performed in house. */
.channel{
  border:1px dashed var(--rule);
  border-left:3px solid var(--steel);
  border-radius:4px;
  background:var(--paper-2);
  padding:clamp(1.4rem,3vw,2.1rem);
  display:grid;
  grid-template-columns:minmax(0,.8fr) minmax(0,1.2fr);
  gap:clamp(1.2rem,4vw,3rem);
  margin-top:clamp(2.4rem,5vw,3.6rem);
  scroll-margin-top:90px; /* clear the sticky header on #parts */
}
@media (max-width:820px){ .channel{ grid-template-columns:1fr; } }
.dark .channel{ background:transparent; border-color:var(--rule-dark); border-left-color:var(--steel); }
.channel__k{
  font-family:var(--mono); font-size:.68rem; letter-spacing:.16em;
  text-transform:uppercase; color:var(--steel); font-weight:600; margin-bottom:.7rem;
}
.dark .channel__k{ color:#7FB6D2; }
.channel h3{ font-size:clamp(1.25rem,1.1rem + .7vw,1.6rem); }
.channel p{ color:var(--text-2); font-size:.95rem; }
.dark .channel p{ color:var(--text-inv-2); }

/* --- Systems we work in ---------------------------------------------- */

.sysgroup{
  display:grid;
  grid-template-columns:minmax(0,190px) minmax(0,1fr);
  gap:1rem clamp(1.2rem,3vw,2.5rem);
  padding:1.25rem 0;
  border-top:1px solid var(--rule);
  align-items:start;
}
.sysgroup:last-of-type{ border-bottom:1px solid var(--rule); }
.dark .sysgroup{ border-color:var(--rule-dark); }
@media (max-width:640px){ .sysgroup{ grid-template-columns:1fr; gap:.7rem; } }
.sysgroup__k{
  font-family:var(--mono); font-size:.68rem; letter-spacing:.13em;
  text-transform:uppercase; color:var(--text-2); padding-top:.35rem;
}
.dark .sysgroup__k{ color:var(--text-inv-2); }
.tags{ display:flex; flex-wrap:wrap; gap:.5rem; list-style:none; margin:0; padding:0; }
.tags li{
  font-size:.9rem; font-weight:520;
  padding:.4rem .8rem;
  border:1px solid var(--rule);
  border-radius:999px;
  background:var(--paper-2);
  white-space:nowrap;
}
.dark .tags li{
  border-color:var(--rule-dark); background:rgba(255,255,255,.04); color:var(--text-inv);
}
.tags li.is-more{
  border-style:dashed; background:transparent; color:var(--text-2); font-weight:400;
}
.dark .tags li.is-more{ color:var(--text-inv-2); }

/* --- CTA band -------------------------------------------------------- */

.cta{
  background:var(--ink-2);
  color:var(--text-inv);
  border-radius:4px;
  padding:clamp(2rem,5vw,3.4rem);
  display:grid; grid-template-columns:1fr auto; gap:2rem; align-items:center;
  position:relative; overflow:hidden;
}
@media (max-width:760px){ .cta{ grid-template-columns:1fr; } }
.cta h2{ color:var(--text-inv); max-width:20ch; }
.cta p{ color:var(--text-inv-2); margin-top:.9rem; }

/* --- Form ------------------------------------------------------------ */

.form{ display:grid; gap:1.1rem; }
.field{ display:grid; gap:.4rem; }
.field label{
  font-family:var(--mono); font-size:.68rem; letter-spacing:.13em;
  text-transform:uppercase; color:var(--text-2);
}
.field input,.field select,.field textarea{
  font:inherit; font-size:.97rem;
  padding:.75rem .85rem;
  border:1px solid var(--rule);
  border-radius:3px;
  background:var(--paper-2);
  color:var(--text);
  width:100%;
}
.field textarea{ min-height:150px; resize:vertical; }
.field input:focus,.field select:focus,.field textarea:focus{
  outline:2px solid var(--amber); outline-offset:1px; border-color:transparent;
}
.field--row{ display:grid; grid-template-columns:1fr 1fr; gap:1.1rem; }
@media (max-width:640px){ .field--row{ grid-template-columns:1fr; } }
.form__note{ font-size:.83rem; color:var(--text-2); margin:0; }
.hp{ position:absolute; left:-9999px; }

.contact-list{ list-style:none; margin:0; padding:0; }
.contact-list li{ padding:1.05rem 0; border-bottom:1px solid var(--rule); }
.contact-list li:first-child{ border-top:1px solid var(--rule); }
.contact-list dt,.contact-list .k{
  font-family:var(--mono); font-size:.66rem; letter-spacing:.14em;
  text-transform:uppercase; color:var(--text-2); display:block; margin-bottom:.3rem;
}
.contact-list a{ text-decoration:none; border-bottom:1px solid var(--amber); }
.contact-list a:hover{ color:var(--amber); }

/* --- Footer ---------------------------------------------------------- */

.site-foot{
  background:var(--ink); color:var(--text-inv-2);
  padding-block:clamp(2.8rem,6vw,4rem) 2rem;
  font-size:.9rem;
}
.foot__grid{
  display:grid; grid-template-columns:1.4fr 1fr 1fr; gap:2rem;
  padding-bottom:2.4rem; border-bottom:1px solid var(--rule-dark);
}
@media (max-width:760px){ .foot__grid{ grid-template-columns:1fr; gap:1.8rem; } }
.foot h4{
  font-family:var(--mono); font-size:.66rem; letter-spacing:.15em;
  text-transform:uppercase; color:var(--text-inv); margin:0 0 .9rem; font-weight:500;
}
.foot ul{ list-style:none; margin:0; padding:0; display:grid; gap:.5rem; }
.foot a{ text-decoration:none; }
.foot a:hover{ color:var(--amber); }
.foot p{ color:var(--text-inv-2); font-size:.9rem; }
.foot__bottom{
  display:flex; flex-wrap:wrap; gap:.6rem 1.5rem; justify-content:space-between;
  padding-top:1.6rem; font-size:.8rem;
}
.foot__bottom span{ font-family:var(--mono); letter-spacing:.06em; }

/* --- Utility --------------------------------------------------------- */

.mt-0{ margin-top:0; }
.stack-lg{ display:grid; gap:1.6rem; }
.skip{
  position:absolute; left:-9999px;
  background:var(--amber); color:#1B1403; padding:.7rem 1.1rem; z-index:100;
}
.skip:focus{ left:.5rem; top:.5rem; }

@media (prefers-reduced-motion:reduce){
  *{ animation:none !important; transition:none !important; scroll-behavior:auto !important; }
}