/* ── Reset & base ──────────────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --clr-bg:      #0f1117;
  --clr-surface: #1a1d27;
  --clr-card:    #20243a;
  --clr-border:  #2e3350;
  --clr-accent:  #4f8ef7;
  --clr-accent2: #f76f4f;
  --clr-text:    #e2e8f0;
  --clr-muted:   #8892aa;
  --clr-green:   #4fd1a5;
  --radius:      8px;
  --transition:  0.2s ease;
}

html { scroll-behavior: smooth; }

body {
  font-family: 'Segoe UI', system-ui, sans-serif;
  background: var(--clr-bg);
  color: var(--clr-text);
  min-height: 100vh;
  line-height: 1.5;
}

/* ── Layout ────────────────────────────────────────────────────────────── */
.page-wrapper {
  max-width: 1280px;
  margin: 0 auto;
  padding: 1.5rem 1rem 3rem;
}

header {
  text-align: center;
  padding: 1.5rem 0 1rem;
  border-bottom: 1px solid var(--clr-border);
  margin-bottom: 1.5rem;
}

header h1 {
  font-size: 1.9rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  background: linear-gradient(135deg, var(--clr-accent), var(--clr-accent2));
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

header p.subtitle {
  color: var(--clr-muted);
  font-size: 0.9rem;
  margin-top: 0.25rem;
}

.main-grid {
  display: grid;
  grid-template-columns: 320px 1fr;
  gap: 1.25rem;
  align-items: start;
}

@media (max-width: 900px) {
  .main-grid { grid-template-columns: 1fr; }
}

/* ── Card ──────────────────────────────────────────────────────────────── */
.card {
  background: var(--clr-card);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 1rem 1.25rem;
}

.card h2 {
  font-size: 0.85rem;
  font-weight: 600;
  letter-spacing: 0.07em;
  text-transform: uppercase;
  color: var(--clr-muted);
  margin-bottom: 0.9rem;
}

/* ── Parameter inputs ──────────────────────────────────────────────────── */
.param-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.55rem;
}

.param-group label {
  display: block;
  font-size: 0.78rem;
  color: var(--clr-muted);
  margin-bottom: 0.2rem;
}

.param-group input[type="number"] {
  width: 100%;
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  color: var(--clr-text);
  padding: 0.35rem 0.5rem;
  font-size: 0.88rem;
  outline: none;
  transition: border-color var(--transition);
}

.param-group input[type="number"]:focus {
  border-color: var(--clr-accent);
}

.section-label {
  grid-column: 1 / -1;
  font-size: 0.72rem;
  color: var(--clr-accent);
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  margin-top: 0.5rem;
}

/* ── Buttons – stable size (no layout shift on active/focus/disabled) ──── */
.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.45rem;
  padding: 0.55rem 1.1rem;
  border: none;
  border-radius: 5px;
  font-size: 0.88rem;
  font-weight: 600;
  cursor: pointer;
  transition: opacity var(--transition), filter var(--transition);
  /* Prevent any state from shifting padding/margin/border */
  outline: none;
  user-select: none;
}

.btn:active   { padding: 0.55rem 1.1rem; border: none; }
.btn:focus    { padding: 0.55rem 1.1rem; border: none; }
.btn:disabled { padding: 0.55rem 1.1rem; border: none; opacity: 0.6; cursor: default; }

.btn-primary {
  background: var(--clr-accent);
  color: #fff;
}
.btn-primary:not(:disabled):hover  { filter: brightness(1.15); }
.btn-primary:not(:disabled):active { filter: brightness(0.9); }

.btn-secondary {
  background: var(--clr-surface);
  color: var(--clr-text);
  border: 1px solid var(--clr-border);
}
.btn-secondary:active   { border: 1px solid var(--clr-border); padding: 0.55rem 1.1rem; }
.btn-secondary:focus    { border: 1px solid var(--clr-border); padding: 0.55rem 1.1rem; }
.btn-secondary:disabled { border: 1px solid var(--clr-border); padding: 0.55rem 1.1rem; }
.btn-secondary:not(:disabled):hover  { background: var(--clr-card); }

.btn-full { width: 100%; margin-top: 0.75rem; }

/* ── Spinner (embedded in button – does NOT change button size) ─────────── */
@keyframes spin { to { transform: rotate(360deg); } }

.spinner {
  display: inline-block;
  width: 0.9em;
  height: 0.9em;
  border: 2px solid rgba(255,255,255,0.3);
  border-top-color: currentColor;
  border-radius: 50%;
  animation: spin 0.65s linear infinite;
  flex-shrink: 0;
}

.spinner-hidden { display: none; }

/* ── Analytic solution panel ───────────────────────────────────────────── */
.solution-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.6rem;
}

@media (max-width: 700px) { .solution-grid { grid-template-columns: 1fr; } }

.sol-row {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  padding: 0.55rem 0.75rem;
  min-height: 2.8rem;
  display: flex;
  align-items: center;
  gap: 0.4rem;
  overflow-x: auto;
}

.sol-row .sol-label {
  color: var(--clr-accent);
  font-size: 0.82rem;
  font-weight: 600;
  white-space: nowrap;
  flex-shrink: 0;
}

.sol-row .katex-display { margin: 0; }

.omega-row {
  grid-column: 1 / -1;
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  padding: 0.45rem 0.75rem;
  display: flex;
  gap: 1.5rem;
  align-items: center;
  font-size: 0.82rem;
  color: var(--clr-muted);
  flex-wrap: wrap;
}

.omega-row strong { color: var(--clr-text); margin-left: 0.25rem; }

/* ── Plot area ─────────────────────────────────────────────────────────── */
.plot-tabs {
  display: flex;
  gap: 0.4rem;
  margin-bottom: 0.75rem;
  flex-wrap: wrap;
}

.tab-btn {
  padding: 0.35rem 0.85rem;
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  background: var(--clr-surface);
  color: var(--clr-muted);
  font-size: 0.82rem;
  cursor: pointer;
  transition: background var(--transition), color var(--transition), border-color var(--transition);
  /* No layout shift on state change */
  outline: none;
}
.tab-btn:active, .tab-btn:focus { padding: 0.35rem 0.85rem; border: 1px solid var(--clr-border); }

.tab-btn.active {
  background: var(--clr-accent);
  color: #fff;
  border-color: var(--clr-accent);
}

.plot-select {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  color: var(--clr-text);
  padding: 0.35rem 0.5rem;
  font-size: 0.88rem;
  outline: none;
  cursor: pointer;
  transition: border-color var(--transition);
}

.plot-select:focus { border-color: var(--clr-accent); }

/* Small tool buttons inside the plot-tabs row */
.plot-tool-btn {
  padding: 0.35rem 0.85rem;
  font-size: 0.82rem;
}

.plot-tool-btn.playing {
  background: var(--clr-accent2);
  color: #fff;
}

/* Animated spring diagram shown below the plot controls */
.anim-diagram-wrap {
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 0.5rem 0.75rem 0.25rem;
  margin-bottom: 0.75rem;
}

.plot-container {
  position: relative;
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: var(--radius);
  padding: 0.75rem;
  min-height: 320px;
}

/* Plot-area spinner overlay */
.plot-spinner-overlay {
  position: absolute;
  inset: 0;
  background: rgba(15,17,23,0.75);
  border-radius: var(--radius);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 0.75rem;
  z-index: 10;
}

.plot-spinner-overlay .big-spinner {
  width: 2.5rem;
  height: 2.5rem;
  border-width: 4px;
  border-color: rgba(255,255,255,0.15);
  border-top-color: var(--clr-accent);
  border-style: solid;
  border-radius: 50%;
  animation: spin 0.8s linear infinite;
}

.plot-spinner-overlay p {
  font-size: 0.82rem;
  color: var(--clr-muted);
}

/* Solution spinner uses an opaque card-color background to fully hide content */
#solution-spinner {
  background: var(--clr-card);
}

/* Plot spinner also needs opaque background so charts don't show through */
#plot-spinner {
  background: var(--clr-card);
}

.plot-hidden { display: none !important; }

/* Idle overlay state: hide spinner animation, show idle message */
.plot-spinner-overlay--idle .big-spinner { display: none; }
.plot-spinner-overlay--idle .overlay-loading-msg { display: none; }
.overlay-idle-msg { display: none; }
.plot-spinner-overlay--idle .overlay-idle-msg { display: block; }

/* Hide/show chart canvases */
.chart-canvas { display: none; }
.chart-canvas.active { display: block; }

/* ── Analysis utilities ────────────────────────────────────────────────── */
.util-grid {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 1rem;
  margin-top: 1.25rem;
}

@media (max-width: 760px) { .util-grid { grid-template-columns: 1fr; } }

.util-card { /* extends .card */ }

.util-form {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 0.55rem;
}

.util-form .full-width { grid-column: 1 / -1; }

.result-box {
  margin-top: 0.75rem;
  background: var(--clr-surface);
  border: 1px solid var(--clr-border);
  border-radius: 5px;
  padding: 0.55rem 0.75rem;
  font-size: 0.88rem;
  min-height: 2.5rem;
}

.result-box .res-label { color: var(--clr-muted); font-size: 0.78rem; }
.result-box .res-value { color: var(--clr-green); font-weight: 600; }
.result-box .res-none  { color: var(--clr-muted); font-style: italic; }

/* Value-at-time table */
.val-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.83rem;
  margin-top: 0.5rem;
}

.val-table th {
  color: var(--clr-muted);
  font-weight: 600;
  text-align: left;
  padding: 0.25rem 0.4rem;
  border-bottom: 1px solid var(--clr-border);
}

.val-table td {
  padding: 0.25rem 0.4rem;
  color: var(--clr-text);
}

.val-table tr:nth-child(even) td { background: rgba(255,255,255,0.02); }

/* ── Diagram ───────────────────────────────────────────────────────────── */
.diagram-svg {
  width: 100%;
  height: 70px;
  display: block;
  margin: 0.5rem 0 0.25rem;
}

/* ── Scrollbar ─────────────────────────────────────────────────────────── */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: var(--clr-bg); }
::-webkit-scrollbar-thumb { background: var(--clr-border); border-radius: 3px; }

/* ── Force warning banner ──────────────────────────────────────────────── */
.force-warning {
  background: rgba(247, 111, 79, 0.12);
  border: 1px solid rgba(247, 111, 79, 0.4);
  border-radius: 5px;
  color: #f7c44f;
  font-size: 0.82rem;
  padding: 0.5rem 0.75rem;
  margin-bottom: 0.75rem;
  line-height: 1.45;
}