/* ── Column Buckling Simulator ─────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg:        #0d1117;
  --surface:   #161b27;
  --surface2:  #1f2535;
  --border:    #2a3050;
  --accent:    #00e5ff;
  --accent-lo: rgba(0,229,255,.22);
  --green:     #3ddc84;
  --red:       #ff5555;
  --gold:      #f5c842;
  --text:      #dde3f0;
  --text-dim:  #6b7a99;
  --font:      'Segoe UI', system-ui, sans-serif;
  --mono:      'Courier New', monospace;
  --radius:    12px;
  --steel:     #78909c;
  --aluminum:  #b0bec5;
  --column-fill: #78909c;
}

body { background: var(--bg); color: var(--text); font-family: var(--font); min-height: 100vh; padding: 0 16px; }
#app { max-width: 980px; margin: 0 auto; display: flex; flex-direction: column; gap: 14px; }

/* ── Header ────────────────────────────────────────────────────── */
header { text-align: center; padding: 4px 0; }
header h1 {
  font-size: 1.8rem; font-weight: 700;
  background: linear-gradient(120deg, #00e5ff 0%, #80deea 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
}
.subtitle { color: var(--text-dim); font-size: 0.85rem; margin-top: 3px; }

/* ── Controls bar ──────────────────────────────────────────────── */
.controls-bar {
  display: flex; flex-wrap: wrap; align-items: center; gap: 14px;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.ctrl-group { display: flex; align-items: center; gap: 8px; }
.ctrl-label { font-size: 0.72rem; text-transform: uppercase; letter-spacing: .06em; color: var(--text-dim); white-space: nowrap; }

.pill-tabs { display: flex; background: var(--bg); border-radius: 8px; padding: 3px; gap: 2px; }
.pill {
  padding: 5px 13px; border: none; background: transparent; color: var(--text-dim);
  border-radius: 6px; cursor: pointer; font-size: 0.81rem;
  transition: background .18s, color .18s, box-shadow .18s;
}
.pill.active { background: var(--accent); color: #fff; box-shadow: 0 0 12px var(--accent-lo); }
.pill:hover:not(.active) { background: var(--surface2); color: var(--text); }

/* ── Canvas card ───────────────────────────────────────────────── */
.canvas-card {
  width: 100%; background: var(--surface);
  border: 1px solid var(--border); border-radius: var(--radius);
  padding: 8px; position: relative; overflow-x: clip;
}
.canvas-card canvas { display: block; width: 100%; height: auto; cursor: default; touch-action: none; }

/* ── Buttons ───────────────────────────────────────────────────── */
.btn {
  padding: 8px 18px; border: none; border-radius: 8px; cursor: pointer;
  font-size: 0.84rem; font-weight: 600; transition: filter .18s, box-shadow .18s, opacity .18s;
}
.btn:disabled { opacity: 0.38; cursor: not-allowed; }
.btn-primary { background: var(--accent); color: #fff; }
.btn-primary:not(:disabled):hover { filter: brightness(1.12); box-shadow: 0 0 12px var(--accent-lo); }
.btn-ghost { background: var(--surface2); color: var(--text); border: 1px solid var(--border); }
.btn-ghost:hover { background: var(--border); }

/* ── Sim controls ─────────────────────────────────────────────── */
.sim-controls {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 14px 18px; display: flex; flex-direction: column; gap: 12px;
}
.sim-row { display: flex; align-items: center; gap: 14px; flex-wrap: wrap; }
.sim-slider-group { display: flex; align-items: center; gap: 10px; flex: 1; min-width: 200px; }
.sim-slider-label { font-size: 0.76rem; font-weight: 700; color: var(--text-dim); white-space: nowrap; min-width: 110px; }
.sim-slider {
  flex: 1; -webkit-appearance: none; appearance: none; height: 6px;
  background: var(--surface2); border-radius: 3px; outline: none;
}
.sim-slider::-webkit-slider-thumb {
  -webkit-appearance: none; width: 18px; height: 18px;
  border-radius: 50%; background: var(--accent); cursor: pointer;
  box-shadow: 0 0 8px var(--accent-lo);
}
.sim-slider::-moz-range-thumb {
  width: 18px; height: 18px; border: none;
  border-radius: 50%; background: var(--accent); cursor: pointer;
}
.sim-slider-val {
  font-family: var(--mono); font-size: 0.9rem; font-weight: 700;
  color: var(--accent); min-width: 75px; text-align: right;
}

/* ── Material selector ─────────────────────────────────────────── */
.mat-row { display: flex; gap: 6px; flex-wrap: wrap; }
.mat-btn {
  padding: 6px 14px; border: 2px solid var(--border); border-radius: 8px;
  background: var(--surface2); color: var(--text-dim); font-size: 0.78rem;
  font-weight: 700; cursor: pointer; display: flex; align-items: center; gap: 6px;
  transition: border-color .18s, color .18s, background .18s;
}
.mat-btn:hover { border-color: var(--accent); color: var(--text); }
.mat-btn.active { border-color: var(--accent); color: #fff; background: rgba(0,229,255,.12); }
.mat-dot {
  width: 10px; height: 10px; border-radius: 50%; flex-shrink: 0;
}

/* ── End condition selector ────────────────────────────────────── */
.end-row { display: flex; gap: 6px; flex-wrap: wrap; }
.end-btn {
  padding: 8px 14px; border: 2px solid var(--border); border-radius: 8px;
  background: var(--surface2); color: var(--text-dim); font-size: 0.76rem;
  font-weight: 700; cursor: pointer; text-align: center;
  transition: border-color .18s, color .18s, background .18s;
}
.end-btn:hover { border-color: var(--accent); color: var(--text); }
.end-btn.active { border-color: var(--accent); color: #fff; background: rgba(0,229,255,.12); }
.end-btn-k { display: block; font-size: 0.68rem; color: var(--accent); margin-top: 2px; font-family: var(--mono); }

/* ── Cross-section selector ────────────────────────────────────── */
.cs-row { display: flex; gap: 6px; flex-wrap: wrap; }
.cs-btn {
  padding: 6px 14px; border: 2px solid var(--border); border-radius: 8px;
  background: var(--surface2); color: var(--text-dim); font-size: 0.78rem;
  font-weight: 700; cursor: pointer;
  transition: border-color .18s, color .18s, background .18s;
}
.cs-btn:hover { border-color: var(--accent); color: var(--text); }
.cs-btn.active { border-color: var(--accent); color: #fff; background: rgba(0,229,255,.12); }

/* ── Readout row ───────────────────────────────────────────────── */
.readout-row {
  display: grid; grid-template-columns: repeat(auto-fill, minmax(130px, 1fr)); gap: 8px;
}
.readout-card {
  background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 8px 12px; text-align: center;
}
.readout-card.big {
  grid-column: span 2; padding: 12px 16px;
}
.readout-label { font-size: 0.62rem; text-transform: uppercase; letter-spacing: .07em; color: var(--text-dim); margin-bottom: 3px; }
.readout-val { font-family: var(--mono); font-size: 1.15rem; font-weight: 700; color: var(--accent); }
.readout-val.big { font-size: 1.6rem; }
.readout-unit { font-size: 0.68rem; color: var(--text-dim); margin-left: 2px; }

/* ── Method badge ──────────────────────────────────────────────── */
.method-badge {
  display: inline-block; padding: 3px 10px; border-radius: 20px; font-size: 0.72rem;
  font-weight: 700; text-transform: uppercase; letter-spacing: .06em;
}
.method-badge.euler { background: rgba(0,229,255,.18); color: #00e5ff; }
.method-badge.johnson { background: rgba(245,200,66,.18); color: #f5c842; }

/* ── Simulate button row ──────────────────────────────────────── */
.sim-btn-row { justify-content: center; gap: 12px; padding: 6px 0; }
.btn-simulate {
  padding: 12px 32px; font-size: 1rem; font-weight: 700;
  background: linear-gradient(135deg, var(--accent) 0%, #00b8d4 100%);
  color: #fff; border: none; border-radius: 10px; cursor: pointer;
  box-shadow: 0 0 18px var(--accent-lo), 0 4px 12px rgba(0,0,0,.3);
  transition: transform .15s, box-shadow .2s, filter .15s;
  letter-spacing: .03em;
}
.btn-simulate:hover { transform: translateY(-2px); box-shadow: 0 0 28px var(--accent-lo), 0 6px 20px rgba(0,0,0,.4); filter: brightness(1.1); }
.btn-simulate:active { transform: translateY(0); }
.btn-simulate:disabled { opacity: 0.4; cursor: not-allowed; transform: none; filter: none; }
.btn-reset {
  padding: 10px 22px; font-size: 0.88rem; font-weight: 600;
  background: var(--surface2); color: var(--text-dim); border: 1px solid var(--border);
  border-radius: 8px; cursor: pointer; transition: background .15s, color .15s;
}
.btn-reset:hover { background: var(--border); color: var(--text); }
.sim-hint { font-size: 0.76rem; color: var(--text-dim); font-style: italic; }

/* ── Verdict banner ───────────────────────────────────────────── */
.verdict-banner {
  display: flex; align-items: center; justify-content: center; gap: 12px;
  padding: 14px 20px; border-radius: var(--radius);
  font-size: 1.1rem; font-weight: 700; letter-spacing: .04em;
  animation: verdictSlide .5s ease-out;
}
.verdict-banner.safe    { background: rgba(61,220,132,.12); border: 2px solid var(--green); color: var(--green); }
.verdict-banner.warning { background: rgba(245,200,66,.12); border: 2px solid var(--gold);  color: var(--gold); }
.verdict-banner.danger  { background: rgba(255,85,85,.12);  border: 2px solid var(--red);   color: var(--red); }
.verdict-icon { font-size: 1.5rem; }
.verdict-text { font-size: 1rem; }
@keyframes verdictSlide { from { opacity: 0; transform: translateY(12px); } to { opacity: 1; transform: translateY(0); } }

/* ── Load bar ──────────────────────────────────────────────────── */
.load-bar-wrap {
  background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 8px 14px;
}
.load-bar-label { font-size: 0.68rem; color: var(--text-dim); text-transform: uppercase; letter-spacing: .06em; margin-bottom: 6px; }
.load-bar-track {
  height: 12px; background: var(--surface2); border-radius: 6px; position: relative; overflow: hidden;
}
.load-bar-fill {
  height: 100%; border-radius: 6px; transition: width .2s, background .2s;
}
.load-bar-fill.safe { background: var(--green); }
.load-bar-fill.warn { background: var(--gold); }
.load-bar-fill.danger { background: var(--red); }
.load-bar-val { font-family: var(--mono); font-size: 0.82rem; font-weight: 700; margin-top: 4px; text-align: right; }

/* ── Explore mode ──────────────────────────────────────────────── */
.item-selector {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 14px 16px;
}
.is-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(155px, 1fr)); gap: 8px; margin-top: 10px; }
.is-btn {
  padding: 10px 14px; border: 2px solid var(--border); border-radius: 10px;
  background: var(--surface2); color: var(--text-dim); font-size: 0.82rem;
  font-weight: 600; cursor: pointer; text-align: left;
  transition: border-color .18s, color .18s, background .18s, box-shadow .18s;
}
.is-btn:hover { border-color: rgba(0,229,255,.45); color: var(--text); }
.is-btn.active { border-color: var(--accent); color: #fff; background: rgba(0,229,255,.15); box-shadow: 0 0 14px var(--accent-lo); }
.is-btn-name { display: block; font-size: 0.82rem; font-weight: 700; }
.is-btn-sym  { display: block; font-size: 0.68rem; color: var(--accent); margin-top: 2px; font-family: var(--mono); }

.item-info {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px 18px; display: flex; flex-direction: column; gap: 8px;
}
.ii-top { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; }
.ii-name { font-size: 1.15rem; font-weight: 800; color: var(--text); }
.ii-cat-badge {
  font-size: 0.62rem; font-weight: 700; text-transform: uppercase;
  letter-spacing: .07em; padding: 3px 10px; border-radius: 20px;
  background: var(--accent-lo); color: var(--accent);
}
.ii-desc { font-size: 0.85rem; color: var(--text-dim); line-height: 1.65; }

.formula-box {
  background: var(--bg); border: 1px solid var(--border); border-radius: 8px;
  padding: 10px 14px; display: flex; align-items: center; gap: 16px; flex-wrap: wrap;
}
.fb-formula { font-family: var(--mono); font-size: 1.1rem; font-weight: 700; color: var(--accent); }
.fb-unit { font-size: 0.78rem; color: var(--text-dim); }

.example-box {
  background: var(--surface2); border: 1px solid var(--border); border-radius: 8px;
  padding: 12px 14px;
}
.example-box h4 { font-size: 0.72rem; text-transform: uppercase; letter-spacing: .08em; color: var(--accent); margin-bottom: 8px; }
.example-box .ex-problem { font-size: 0.84rem; color: var(--text); margin-bottom: 8px; line-height: 1.6; }
.example-box .ex-step { font-size: 0.8rem; color: var(--text-dim); line-height: 1.6; padding: 2px 0; }
.example-box .ex-step strong { color: var(--green); font-family: var(--mono); }

/* ── Practice mode ─────────────────────────────────────────────── */
.practice-panel {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px 18px;
}
.pp-prompt { font-size: 0.92rem; font-weight: 600; color: var(--text); margin-bottom: 14px; line-height: 1.6; }
.pp-input-row { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; }
.pp-input {
  flex: 1; min-width: 120px; max-width: 220px;
  padding: 10px 14px; border: 2px solid var(--border); border-radius: 8px;
  background: var(--bg); color: var(--text); font-family: var(--mono);
  font-size: 1rem; font-weight: 700; transition: border-color .18s;
}
.pp-input:focus { outline: none; border-color: var(--accent); }
.pp-unit { font-size: 0.88rem; color: var(--text-dim); font-weight: 600; }
.pp-bottom { display: flex; align-items: center; gap: 12px; flex-wrap: wrap; margin-top: 14px; }
.feedback { font-size: 0.88rem; font-weight: 600; }
.feedback.ok  { color: var(--green); }
.feedback.err { color: var(--red); }

.solution-panel {
  background: var(--surface2); border: 1px solid var(--border); border-radius: 8px;
  padding: 14px 16px; margin-top: 12px;
}
.solution-panel h4 { font-size: 0.72rem; text-transform: uppercase; letter-spacing: .08em; color: var(--accent); margin-bottom: 8px; }
.sol-step { font-size: 0.82rem; color: var(--text-dim); line-height: 1.7; padding: 2px 0; }
.sol-step strong { color: var(--green); font-family: var(--mono); }

.practice-bar {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.pbar-score { font-size: 0.84rem; color: var(--text-dim); margin-left: auto; white-space: nowrap; }
.pbar-score span { color: var(--text); font-weight: 700; }

/* ── Quiz panels ───────────────────────────────────────────────── */
.question-panel {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 16px 18px;
}
.qp-prompt { font-size: 0.88rem; font-weight: 600; color: var(--text); margin-bottom: 12px; line-height: 1.6; }
.answer-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; }
.answer-btn {
  padding: 14px 16px; border: 2px solid var(--border); border-radius: 10px;
  background: var(--surface2); color: var(--text); font-size: 0.88rem;
  font-weight: 600; cursor: pointer; text-align: center;
  transition: border-color .18s, background .18s, color .18s, transform .12s;
}
.answer-btn:hover:not(.locked) { border-color: var(--accent); background: rgba(0,229,255,.06); }
.answer-btn.correct { border-color: var(--green); background: rgba(61,220,132,.12); color: var(--green); }
.answer-btn.wrong { border-color: var(--red); background: rgba(255,85,85,.08); color: var(--red); }
.answer-btn.locked { cursor: default; opacity: 0.6; }
.answer-btn.correct.locked { opacity: 1; }

.quiz-input-row { display: flex; align-items: center; gap: 10px; flex-wrap: wrap; margin-bottom: 10px; }
.qi-input {
  flex: 1; min-width: 120px; max-width: 200px;
  padding: 10px 14px; border: 2px solid var(--border); border-radius: 8px;
  background: var(--bg); color: var(--text); font-family: var(--mono);
  font-size: 1rem; font-weight: 700; transition: border-color .18s;
}
.qi-input:focus { outline: none; border-color: var(--accent); }
.qi-unit { font-size: 0.84rem; color: var(--text-dim); font-weight: 600; }

.quiz-bar {
  display: flex; align-items: center; gap: 12px; flex-wrap: wrap;
  padding: 12px 16px;
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
}
.qbar-counter { display: flex; align-items: baseline; gap: 3px; background: var(--bg); border: 1px solid var(--border); border-radius: 8px; padding: 4px 12px; }
.qbar-q-label { font-size: 0.7rem; font-weight: 700; color: var(--accent); text-transform: uppercase; letter-spacing: .08em; }
.qbar-q-num { font-family: var(--mono); font-size: 1.3rem; font-weight: 700; color: var(--text); line-height: 1; }
.qbar-q-sep { font-size: 0.82rem; color: var(--text-dim); }
.qbar-q-total { font-family: var(--mono); font-size: 0.88rem; color: var(--text-dim); }
.quiz-feedback { font-size: 0.88rem; font-weight: 600; }
.quiz-feedback.ok  { color: var(--green); }
.quiz-feedback.err { color: var(--red); }

/* Quiz result */
.quiz-result {
  background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius);
  padding: 20px 22px; display: flex; flex-direction: column; gap: 14px;
}
.qr-header { display: flex; align-items: flex-start; justify-content: space-between; }
.qr-title-wrap { display: flex; flex-direction: column; gap: 5px; }
.qr-title  { font-size: 1.1rem; font-weight: 700; color: var(--text); }
.qr-stars  { font-size: 1.2rem; letter-spacing: 3px; }
.qr-score-wrap { text-align: right; }
.qr-score { font-family: var(--mono); font-size: 2.2rem; font-weight: 700; line-height: 1; text-shadow: 0 0 14px currentColor; }
.qr-score.perfect { color: var(--gold); }
.qr-score.good { color: var(--green); }
.qr-score.poor { color: var(--red); }
.qr-verdict { font-size: 0.72rem; color: var(--text-dim); margin-top: 3px; }
.qr-rows { display: flex; flex-direction: column; gap: 7px; }
.qr-row {
  display: grid; grid-template-columns: 30px 1fr 26px; align-items: center; gap: 10px;
  background: var(--surface2); border: 1px solid var(--border); border-left-width: 3px;
  border-radius: 8px; padding: 9px 12px;
}
.qr-row.ok  { border-left-color: var(--green); }
.qr-row.err { border-left-color: var(--red); }
.qr-qnum { font-size: 0.72rem; font-weight: 700; color: var(--accent); }
.qr-detail { font-size: 0.78rem; color: var(--text-dim); }
.qr-detail strong { color: var(--text); }
.qr-mark { text-align: right; font-size: 1rem; font-weight: 700; }
.qr-row.ok .qr-mark { color: var(--green); }
.qr-row.err .qr-mark { color: var(--red); }

/* ── SEO Article ───────────────────────────────────────────────── */
.seo-article { background: var(--surface); border: 1px solid var(--border); border-radius: var(--radius); padding: 22px 24px; line-height: 1.7; }
.seo-article h2 { font-size: 1.25rem; color: var(--text); margin-bottom: 12px; }
.seo-article h3 { font-size: 1.05rem; color: var(--accent); margin: 16px 0 6px; }
.seo-article p { font-size: 0.88rem; color: var(--text-dim); margin-bottom: 10px; }

/* ── Responsive ────────────────────────────────────────────────── */
@media (max-width: 768px) {
  .answer-grid { grid-template-columns: 1fr 1fr; }
  .is-grid { grid-template-columns: repeat(auto-fill, minmax(130px, 1fr)); }
  .controls-bar { gap: 10px; }
  .readout-row { grid-template-columns: repeat(2, 1fr); }
  .sim-slider-group { min-width: 160px; }
  .mat-row, .end-row, .cs-row { gap: 4px; }
  .mat-btn, .end-btn, .cs-btn { padding: 5px 10px; font-size: 0.72rem; }
}
@media (max-width: 500px) {
  header h1 { font-size: 1.4rem; }
  .subtitle  { font-size: 0.78rem; }
  .controls-bar { padding: 10px 12px; gap: 8px; }
  .pill { padding: 5px 10px; font-size: 0.76rem; }
  .answer-grid { grid-template-columns: 1fr; }
  .is-grid { grid-template-columns: 1fr 1fr; }
  .readout-row { grid-template-columns: 1fr 1fr; }
  .sim-slider-group { min-width: 100%; }
  .mat-btn, .end-btn, .cs-btn { padding: 4px 8px; font-size: 0.68rem; }
  .readout-card.big { grid-column: span 1; }
}