/* ── CSS Variables ───────────────────────────────────────────────────────────── */
:root {
  --bg:  #0d0f1a;
  --bg2: #13162a;
  --bg3: #292e43;
  --b1:  rgba(255,255,255,0.08);
  --b2:  rgba(255,255,255,0.14);
  --t1:  #e8eaf6;
  --t2:  #8892b0;
  --t3:  #4a5278;
  --blue: #d0dff8;
  --bbg:  rgba(79,142,247,0.12);
  --bbd:  rgba(79,142,247,0.35);
  --teal: #2dd4bf;
  --tbg:  rgba(45,212,191,0.12);
  --org:  #fb923c;
  --obg:  rgba(251,146,60,0.12);
  --grn:  #4ade80;
  --gbg:  rgba(74,222,128,0.12);
  --pur:  #a78bfa;
  --pbg:  rgba(167,139,250,0.12);
  --red:  #f87171;
  --rbg:  rgba(248,113,113,0.12);
  --mono: 'JetBrains Mono', monospace;
}
/*Reset & Base*/
* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
body {
  font-family: 'Syne', sans-serif;
  background: var(--bg);
  color: var(--t1);
  min-height: 100vh;
  overflow-x: hidden;
}
/*Dot-grid background*/
body::before {
  content: '';
  position: fixed;
  inset: 0;
  background-image: radial-gradient(circle, rgba(79,142,247,.08) 1px, transparent 1px);
  background-size: 28px 28px;
  pointer-events: none;
  z-index: 0;
}
/*Layout*/
.wrap {
  position: relative;
  z-index: 1;
  padding: 2rem 0 4rem;
}

/* Typography */
h1 {
  font-size: clamp(2rem, 5vw, 3.2rem);
  font-weight: 700;
  letter-spacing: -.02em;
  text-align: center;
  margin-bottom: .4rem;
}
h1 span { color: var(--blue); }
.sub {
  font-family: var(--mono);
  font-size: .75rem;
  color: var(--t3);
  letter-spacing: .12em;
  text-transform: uppercase;
  text-align: center;
  margin-bottom: 2rem;
}
/*DS Selector Buttons*/
.ds-sel {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
  justify-content: center;
  margin-bottom: 1.5rem;
}
.db {
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: .06em;
  padding: 7px 16px;
  border-radius: 6px;
  border: 1px solid var(--b2);
  background: var(--bg2);
  color: var(--t2);
  cursor: pointer;
  transition: all .18s;
  text-transform: uppercase;
}
.db:hover { border-color: var(--bbd); color: var(--blue); }
.db.active { background: var(--bbg); border-color: var(--bbd); color: var(--blue); }

/*Panel*/
.panel {
  background: var(--bg2);
  border: 1px solid var(--b1);
  border-radius: 16px;
  overflow: hidden;
}

/* Panel Header */
.ph {
  background: var(--bg3);
  border-bottom: 1px solid var(--b1);
  padding: 1rem 1.5rem;
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  align-items: center;
}

.ptitle {
  font-family: var(--mono);
  font-size: 12px;
  font-weight: 500;
  color: var(--blue);
  text-transform: uppercase;
  letter-spacing: .1em;
  margin-right: auto;
}
/*Form Controls*/
input.ci {
  font-family: var(--mono);
  font-size: 13px;
  padding: 7px 12px;
  border-radius: 8px;
  border: 1px solid var(--b2);
  background: var(--bg);
  color: var(--t1);
  outline: none;
  transition: border-color .18s;
}
input.ci:focus        { border-color: var(--bbd); }
input.ci::placeholder { color: var(--t3); }
button.cb {
  font-family: var(--mono);
  font-size: 11px;
  font-weight: 500;
  letter-spacing: .06em;
  padding: 7px 14px;
  border-radius: 8px;
  border: 1px solid var(--b2);
  background: var(--bg);
  color: var(--t2);
  cursor: pointer;
  transition: all .18s;
  text-transform: uppercase;
  white-space: nowrap;
}
button.cb:hover   { background: var(--bg3); color: var(--t1); }
button.cb:active  { transform: scale(.97); }
button.cb:disabled { opacity: .4; cursor: not-allowed; }
/*Button colour variants*/
.cp { background: var(--bbg); border-color: var(--bbd);              color: var(--blue); }
.cs { background: var(--gbg); border-color: rgba(74,222,128,.3);     color: var(--grn);  }
.cd { background: var(--rbg); border-color: rgba(248,113,113,.3);    color: var(--red);  }
.ct { background: var(--tbg); border-color: rgba(45,212,191,.3);     color: var(--teal); }
/*Speed slider*/
.spd {
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--mono);
  font-size: 11px;
  color: var(--t3);
}
.spd input { width: 90px; accent-color: var(--blue); }
.sv        { color: var(--blue); min-width: 16px; text-align: center; }
/*Visualization Canvas*/
#vc {
  padding: 1.5rem;
  min-height: 220px;
  display: flex;
  align-items: flex-end;
}
/*Bar Chart (Sorting)*/
.bars {
  display: flex;
  align-items: flex-end;
  gap: 4px;
  height: 180px;
  width: 100%;
  padding-bottom: 2px;
}
.bw {
  display: flex;
  flex-direction: column;
  align-items: center;
  flex: 1;
  height: 100%;
  justify-content: flex-end;
  gap: 4px;
}
.br {
  width: 100%;
  border-radius: 4px 4px 0 0;
  transition: height .18s, background .18s;
  min-height: 4px;
}
.bn {
  font-family: var(--mono);
  font-size: 10px;
  color: var(--t3);
  text-align: center;
}
/*Bar colour states*/
.c-def { background: rgba(79,142,247,.55); }
.c-cmp { background: var(--red);  }
.c-swp { background: var(--org);  }
.c-srt { background: var(--grn);  }
.c-pvt { background: var(--pur);  }
.c-min { background: var(--teal); }

/*Linked List*/
.lla {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 6px;
  min-height: 80px;
  width: 100%;
  padding: .5rem 0;
}
.lln {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 3px;
}
.llt {
  font-family: var(--mono);
  font-size: 9px;
  text-transform: uppercase;
  letter-spacing: .08em;
  color: var(--blue);
  height: 14px;
}
.llb {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 52px;
  height: 52px;
  border-radius: 10px;
  border: 1.5px solid var(--bbd);
  background: var(--bbg);
  font-family: var(--mono);
  font-size: 15px;
  font-weight: 500;
  color: var(--blue);
}
.llarr {
  font-size: 18px;
  color: var(--t3);
  margin-top: 17px;
}
.llnull {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 48px;
  height: 52px;
  border-radius: 10px;
  border: 1px dashed var(--b2);
  font-family: var(--mono);
  font-size: 11px;
  color: var(--t3);
  margin-top: 17px;
}
/*Stack*/
.ska {
  display: flex;
  align-items: flex-end;
  gap: 24px;
  min-height: 180px;
  padding: .5rem 0;
}
.skc {
  display: flex;
  flex-direction: column-reverse;
  align-items: center;
  gap: 4px;
}
.skbase {
  width: 88px;
  height: 3px;
  background: var(--b2);
  border-radius: 2px;
  margin-top: 4px;
}
.skn {
  width: 88px;
  height: 46px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 8px;
  font-family: var(--mono);
  font-size: 15px;
  font-weight: 500;
  border: 1.5px solid var(--bbd);
  background: var(--bbg);
  color: var(--blue);
  animation: ni .3s ease;
}
.skn.top {
  border-color: rgba(167,139,250,.5);
  background: var(--pbg);
  color: var(--pur);
}
.skl {
  display: flex;
  flex-direction: column-reverse;
  gap: 4px;
  padding-bottom: 7px;
}
.sll {
  height: 46px;
  display: flex;
  align-items: center;
  font-family: var(--mono);
  font-size: 10px;
  color: var(--t3);
  letter-spacing: .06em;
}
.sll.tl { color: var(--pur); }
/*Queue*/
.qua {
  display: flex;
  flex-direction: column;
  gap: 12px;
  min-height: 100px;
  padding: .5rem 0;
  width: 100%;
}
.qtags {
  display: flex;
  align-items: center;
  gap: 6px;
  flex-wrap: wrap;
}
.qt {
  font-family: var(--mono);
  font-size: 10px;
  text-transform: uppercase;
  letter-spacing: .08em;
  padding: 3px 10px;
  border-radius: 4px;
  border: 1px solid;
}
.qf { color: var(--teal); border-color: rgba(45,212,191,.3);  background: var(--tbg); }
.qr { color: var(--org);  border-color: rgba(251,146,60,.3);  background: var(--obg); }
.qnodes {
  display: flex;
  align-items: center;
  flex-wrap: wrap;
  gap: 6px;
}
.qn {
  display: flex;
  align-items: center;
  justify-content: center;
  min-width: 52px;
  height: 52px;
  border-radius: 10px;
  font-family: var(--mono);
  font-size: 15px;
  font-weight: 500;
  border: 1.5px solid;
  animation: ni .3s ease;
}
.qn.front { background: var(--tbg); border-color: rgba(45,212,191,.4); color: var(--teal); }
.qn.rear  { background: var(--obg); border-color: rgba(251,146,60,.4);  color: var(--org);  }
.qn.mid   { background: var(--bbg); border-color: var(--bbd);           color: var(--blue); }
.qarr { font-size: 16px; color: var(--t3); }
/*Legend*/
.leg {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  padding: .75rem 1.5rem;
  border-top: 1px solid var(--b1);
  background: var(--bg3);
}
.li {
  display: flex;
  align-items: center;
  gap: 6px;
  font-family: var(--mono);
  font-size: 10px;
  color: var(--t3);
  text-transform: uppercase;
  letter-spacing: .06em;
}
.ld {
  width: 10px;
  height: 10px;
  border-radius: 3px;
  flex-shrink: 0;
}
/*Log Bar*/
#log {
  border-top: 1px solid var(--b1);
  padding: .75rem 1.5rem;
  background: var(--bg);
  font-family: var(--mono);
  font-size: 12px;
  color: var(--t2);
  min-height: 40px;
  border-radius: 0 0 16px 16px;
}
#log .op  { color: var(--blue);  }
#log .val { color: var(--teal);  }
#log .ok  { color: var(--grn);   }
#log .err { color: var(--red);   }
/*Utility*/
.empty {
  width: 100%;
  text-align: center;
  padding: 2rem;
  font-family: var(--mono);
  font-size: 12px;
  color: var(--t3);
}
/*Animation*/
@keyframes ni {
  from { transform: scale(.6); opacity: 0; }
  to   { transform: scale(1);  opacity: 1; }
}
/*Responsive*/
@media (max-width: 576px) {
  .ph             { gap: 6px; }
  .cb, .ci        { font-size: 10px; padding: 6px 10px; }
  .bars           { height: 140px; }
}