/* ================================================================
   Conservation of Mechanical Energy — Design System
   Matching the Hooke's Law / Collisions simulation style
   ================================================================ */
@import url("https://fonts.googleapis.com/css2?family=Inter:wght@500;600;700&family=IBM+Plex+Sans:wght@400;500;600;700&display=swap");

:root {
  --bg-950: #090b0f;
  --bg-900: #11141b;
  --bg-800: #1e2430;
  --text-100: #eef2f9;
  --text-300: #c9d1df;
  --text-500: #a9b2c3;
  --gold-500: #c8a24a;
  --gold-400: #d8b767;
  --gold-300: #e5cc8f;
  --surface: rgba(17, 20, 27, 0.93);
  --surface-alt: rgba(30, 36, 48, 0.9);
  --border: rgba(229, 204, 143, 0.22);
  --shadow-lg: 0 16px 32px rgba(0, 0, 0, 0.4);
  --app-bg: radial-gradient(circle at 16% 10%, #2b364d 0%, #1d2433 38%, #0b0e15 100%);
  --panel-text-strong: #fff5df;
  --rail-tick: #f1dc9d;
  --success: #5cbf79;
  --danger: #ff5f7a;
  --pe-color: #4a9eff;
  --ke-color: #ff8c42;
  --me-color: #5cbf79;
}

:root {
  --bg-950: #e9f4fb;
  --bg-900: #fff4dd;
  --bg-800: #ffffff;
  --text-100: #123140;
  --text-300: #4b6570;
  --text-500: #4b6570;
  --gold-500: #0f7e9b;
  --gold-400: #0b5f77;
  --gold-300: #d67b19;
  --surface: rgba(255, 255, 255, 0.96);
  --surface-alt: rgba(247, 252, 255, 0.98);
  --border: #c8dbe3;
  --shadow-lg: 0 12px 24px rgba(12, 54, 68, 0.12);
  --app-bg:
    radial-gradient(1200px 700px at 8% 2%, rgba(19, 143, 176, 0.18), transparent 62%),
    radial-gradient(900px 600px at 92% 98%, rgba(220, 132, 32, 0.18), transparent 66%),
    linear-gradient(165deg, #e9f4fb, #fff4dd);
  --panel-text-strong: #123140;
  --rail-tick: #123140;
  --pe-color: #2979ff;
  --ke-color: #e65100;
  --me-color: #2e7d32;
}

*, *::before, *::after { box-sizing: border-box; }
html, body { margin: 0; min-height: 100%; }

body {
  font-family: "Inter", "IBM Plex Sans", "Segoe UI", sans-serif;
  color: var(--text-100);
  background: var(--app-bg);
  line-height: 1.45;
  overflow-x: hidden;
}

canvas { will-change: transform; transform: translateZ(0); }

/* ===== Background Grid ===== */
.bg-grid {
  position: fixed; inset: 0; z-index: -1;
  background-image:
    linear-gradient(rgba(229, 204, 143, 0.07) 1px, transparent 1px),
    linear-gradient(90deg, rgba(229, 204, 143, 0.07) 1px, transparent 1px);
  background-size: 44px 44px;
  mask-image: radial-gradient(circle at center, black 42%, transparent 95%);
}

.bg-grid {
  background-image: linear-gradient(rgba(15, 126, 155, 0.06) 1px, transparent 1px),
    linear-gradient(90deg, rgba(214, 123, 25, 0.06) 1px, transparent 1px);
}

h1, h2, h3, h4 { margin: 0; font-family: "Inter", "IBM Plex Sans", "Segoe UI", sans-serif; }

/* ===== Shell ===== */
.shell { width: min(1480px, calc(100% - 2rem)); margin-inline: auto; }

/* ===== Hero ===== */
.hero {
  margin-top: 1.2rem;
  border: 1px solid var(--border);
  border-radius: 14px;
  padding: 1.2rem 1.4rem;
  padding-right: 12.5rem;
  background: linear-gradient(130deg, rgba(20, 25, 36, 0.95), rgba(11, 13, 19, 0.95));
  box-shadow: var(--shadow-lg);
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: ""; position: absolute; inset: 0 auto 0 0;
  width: 12px; background: var(--gold-500); border-radius: 14px 0 0 14px;
}
.hero {
  background: linear-gradient(160deg, #ffffff, #f7fbfd);
  border-color: #c8dbe3;
}
.kicker {
  margin: 0; font-size: 0.8rem; text-transform: uppercase;
  letter-spacing: 0.1em; color: var(--gold-400); font-weight: 700;
}
.hero h1 {
  font-size: clamp(1.8rem, 2.4vw, 3rem);
  margin-top: 0.35rem; color: var(--panel-text-strong);
  line-height: 1.05; overflow-wrap: anywhere;
}
.subtitle { margin: 0.38rem 0 0; color: var(--text-300); max-width: 75ch; }
.hero-top {
  display: flex; align-items: flex-start; justify-content: space-between; gap: 1rem;
}
.hero-top > :first-child { flex: 1 1 auto; min-width: 0; padding-left: 0.4rem; }
/* ===== Mode Tabs ===== */
.mode-tabs {
  display: flex; gap: 0.55rem; margin-top: 0.9rem;
}
.mode-tab {
  flex: 1; font-weight: 700; font-size: 1.05rem;
  text-align: center; border-radius: 10px; padding: 0.62rem 0.82rem;
  /* Default (inactive) — plain ghost style */
  background: rgba(200, 162, 74, 0.10);
  color: var(--text-300);
  border: 1px solid var(--border);
  transition: background 0.2s, color 0.2s, border-color 0.2s;
}
.mode-tab:hover:not(.active) {
  background: rgba(200, 162, 74, 0.18);
  color: var(--text-100);
}
.mode-tab.active {
  background: linear-gradient(135deg, var(--gold-500), var(--gold-400));
  color: #2b1d06;
  border-color: var(--gold-500);
  filter: none;
}
.mode-tab {
  background: #f0f8fb;
  color: var(--text-300);
  border-color: #c8dbe3;
}
.mode-tab:hover:not(.active) {
  background: #dff0f6;
  color: var(--text-100);
}
.mode-tab.active {
  background: linear-gradient(135deg, #0d839f, #0b5f77);
  color: #ffffff;
  border-color: #0a5d74;
}
.mode-content { display: none; }
.mode-content.active { display: block; }

/* ===== Layout ===== */
.app-layout {
  margin-top: 0.9rem; margin-bottom: 0.6rem;
  display: grid; gap: 0.9rem;
  grid-template-columns: repeat(12, minmax(0, 1fr));
}

/* ===== Panels ===== */
.panel {
  border: 1px solid var(--border); border-radius: 12px;
  background: var(--surface); padding: 1rem;
  box-shadow: 0 8px 22px rgba(0, 0, 0, 0.28);
}
.panel {
  box-shadow: 0 6px 16px rgba(12, 54, 68, 0.08);
}
.full { grid-column: span 12; }
.wide { grid-column: span 8; }
.narrow { grid-column: span 4; }

/* ===== Inquiry Cards ===== */
.inquiry-grid {
  margin-top: 0.8rem; display: grid; gap: 0.7rem;
  grid-template-columns: repeat(3, minmax(0, 1fr));
}
.inquiry-card {
  border: 1px solid var(--border); border-radius: 10px;
  padding: 0.75rem; background: var(--surface-alt);
}
.inquiry-card h3 { font-size: 1.05rem; margin-bottom: 0.34rem; }
.inquiry-card p { color: var(--text-300); margin: 0; }
.inquiry-card strong { color: var(--gold-300); }

/* ===== Buttons ===== */
button {
  border: 1px solid var(--gold-500); border-radius: 10px;
  background: linear-gradient(135deg, var(--gold-500), var(--gold-400));
  color: #2b1d06; font-weight: 700; font: inherit;
  padding: 0.58rem 0.82rem; cursor: pointer;
  transition: filter 0.15s;
}
button:hover { filter: brightness(1.06); }
button.ghost {
  background: rgba(200, 162, 74, 0.12);
  color: var(--text-100);
}
button:disabled { opacity: 0.45; cursor: not-allowed; filter: none; }
button {
  background: linear-gradient(160deg, #0d839f, #0b5f77);
  color: #ffffff; border-color: #0a5d74;
}
button.ghost {
  background: #f6fbfd; color: var(--text-100); border-color: #9dbac5;
}
.button-row {
  margin-top: 0.7rem; display: flex; flex-wrap: wrap; gap: 0.55rem;
}
.button-row button { flex: 1 1 0; min-width: 0; }

/* ===== Inputs / Sliders ===== */
input, select, output { font: inherit; }
input, select, output {
  border: 1px solid var(--border); border-radius: 10px;
  background: var(--surface-alt); color: var(--text-100);
  padding: 0.54rem 0.62rem;
}
input,
select,
output {
  background: #f9fdff; color: var(--text-100); border-color: #a9c4cf;
}
label {
  display: flex; flex-direction: column; gap: 0.45rem;
  font-size: 0.92rem; color: var(--text-300);
}
.control-note { font-size: 0.82rem; line-height: 1.35; color: var(--text-500); }
.range-row {
  display: grid; grid-template-columns: 1fr auto;
  align-items: center; gap: 0.5rem;
}
.range-row output {
  min-width: 5ch; text-align: right; color: var(--gold-300);
  border: none; background: transparent; padding: 0;
  font-weight: 700; letter-spacing: 0.02em;
}

/* ===== Compact Toggle ===== */
.compact-toggle {
  display: flex !important; flex-direction: row !important;
  align-items: center; gap: 0.45rem; min-height: 38px; padding: 0.2rem 0;
}
.compact-toggle input { width: 1rem; height: 1rem; margin: 0; }

/* ===== Sim Canvas ===== */
.sim-canvas {
  width: 100%; border: 1px solid var(--border); border-radius: 12px;
  background: radial-gradient(circle at 12% 12%, rgba(223, 190, 115, 0.14), transparent 34%),
    linear-gradient(180deg, #0d1118 0%, #090b0f 100%);
}
.sim-canvas {
  background: linear-gradient(180deg, #f8fcff, #f2f8fb);
  border-color: #b8d1db;
}
.graph-canvas { margin-top: 0.5rem; }
.graph-canvas-sm { height: 240px; }
.graph-pair {
  display: grid; grid-template-columns: 1fr 1fr;
  gap: 0.8rem; margin-top: 0.5rem;
}

/* ===== Sim Toolbar ===== */
.sim-toolbar {
  display: flex; flex-wrap: wrap; align-items: flex-start;
  justify-content: space-between; gap: 0.75rem; margin-bottom: 0.7rem;
}
.sim-toolbar h2 { color: var(--panel-text-strong); }
.sim-toolbar .hint { margin: 0; flex: 1 1 280px; }
.hint { margin: 0.6rem 0 0; color: var(--text-300); font-size: 0.92rem; }

/* ===== Metric Cards ===== */
.metric-grid {
  margin-top: 0.7rem; display: grid; gap: 0.55rem;
}
.readout-grid { grid-template-columns: repeat(4, 1fr); }
.metric-card {
  border: 1px solid var(--border); border-left: 5px solid var(--gold-500);
  background: var(--surface-alt); border-radius: 10px;
  padding: 0.62rem 0.7rem;
}
.metric-card {
  background: linear-gradient(170deg, #f7fcff, #f1f9fd);
  border-color: #b8d1db;
}
.metric-line {
  display: flex; justify-content: space-between; align-items: baseline;
  gap: 0.6rem; color: var(--text-300);
}
.metric-line span:last-child { color: var(--text-100); font-weight: 700; }

/* ===== Energy Readout Grid ===== */
.energy-readout-grid {
  display: grid; grid-template-columns: repeat(3, 1fr);
  gap: 0.5rem; margin-top: 0.5rem;
}
.energy-card {
  border-radius: 10px; padding: 0.55rem 0.6rem;
  text-align: center; border: 1px solid var(--border);
  background: var(--surface-alt);
}
.energy-card .energy-label {
  display: block; font-size: 0.78rem; font-weight: 700;
  text-transform: uppercase; letter-spacing: 0.06em; margin-bottom: 0.2rem;
}
.energy-card .energy-value {
  display: block; font-size: 1.05rem; font-weight: 700;
}
.pe-card { border-left: 4px solid var(--pe-color); }
.pe-card .energy-label { color: var(--pe-color); }
.pe-card .energy-value { color: var(--pe-color); }
.ke-card { border-left: 4px solid var(--ke-color); }
.ke-card .energy-label { color: var(--ke-color); }
.ke-card .energy-value { color: var(--ke-color); }
.me-card { border-left: 4px solid var(--me-color); }
.me-card .energy-label { color: var(--me-color); }
.me-card .energy-value { color: var(--me-color); }

/* ===== Data Table ===== */
.section-title {
  margin: 0.9rem 0 0.4rem; font-size: 1.05rem; color: var(--gold-300);
}
.data-table-wrap { overflow-x: auto; }
.data-table {
  width: 100%; border-collapse: collapse; font-size: 0.85rem;
}
.data-table th {
  background: rgba(200, 162, 74, 0.18);
  color: var(--gold-300); padding: 0.5rem 0.4rem; text-align: center;
  font-weight: 700; font-size: 0.8rem; border-bottom: 1px solid var(--border);
}
.data-table td {
  padding: 0.4rem; text-align: center; color: var(--text-500);
  border-bottom: 1px solid rgba(229, 204, 143, 0.1);
}
.data-table tr.recorded td {
  color: var(--text-100); font-weight: 600;
  background: rgba(200, 162, 74, 0.08);
}

/* ===== Mass Controls ===== */
.mass-controls-box {
  margin-top: 0.6rem; padding: 0.7rem;
  border: 1px solid var(--border); border-radius: 10px;
  background: var(--surface-alt);
}

/* ===== Teacher Annotation ===== */
.teacher-annotation {
  margin-top: 0.8rem; padding: 0.8rem;
  border: 1px solid var(--me-color);
  border-left: 5px solid var(--me-color);
  border-radius: 10px;
  background: rgba(92, 191, 121, 0.08);
  font-size: 0.92rem;
  color: var(--text-300);
  min-height: 60px;
}
.teacher-annotation p { margin: 0; }
.teacher-annotation strong { color: var(--me-color); }

/* ===== Tab Navigation ===== */
.tab-nav {
  display: flex; gap: 0; border-bottom: 2px solid var(--border);
}
.tab-btn {
  flex: 1; padding: 0.7rem 0.8rem; background: transparent;
  border: none; border-bottom: 3px solid transparent;
  cursor: pointer; font-weight: 600; color: var(--text-500);
  transition: all 0.25s; border-radius: 0;
}
.tab-btn:hover { color: var(--text-100); background: rgba(128, 128, 128, 0.05); }
.tab-btn.active {
  color: var(--gold-300); border-bottom-color: var(--gold-500);
  background: transparent;
}
.tab-btn {
  background: transparent;
  color: var(--text-500);
}
.tab-btn:hover {
  color: var(--text-100);
}
.tab-btn.active {
  color: var(--gold-400); border-bottom-color: var(--gold-400);
}
.tab-content { display: none; }
.tab-content.active { display: block; }

/* ===== Theory layout ===== */
.theory-columns {
  display: grid; grid-template-columns: 1fr 1fr; gap: 1.5rem;
  margin-top: 0.8rem;
}
.theory-columns h3 { color: var(--gold-300); margin-bottom: 0.3rem; font-size: 1.1rem; }
.theory-columns p { color: var(--text-300); margin: 0.4rem 0; }
.theory-columns ul { color: var(--text-300); margin: 0.4rem 0 0.4rem 1.2rem; }
.theory-columns li { margin-bottom: 0.5rem; }
.theory-columns strong { color: var(--gold-300); }
.equation {
  background: var(--surface-alt); padding: 0.8rem 1rem;
  margin: 0.6rem 0; border-left: 4px solid var(--gold-500);
  border-radius: 8px; font-size: 1.05rem; overflow-x: auto;
}

/* ===== Footer ===== */
footer {
  text-align: center; color: var(--text-500); padding: 1.5rem;
  margin-top: 1rem; font-size: 0.88rem;
}

/* ===== Accessibility ===== */
.sr-only {
  position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px;
  overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border-width: 0;
}

/* ===== Focus ===== */
button:focus-visible,
input:focus-visible,
select:focus-visible,
output:focus-visible {
  outline: 2px solid var(--gold-400); outline-offset: 2px;
}

/* ===== Responsive ===== */
@media (max-width: 1180px) {
  .inquiry-grid, .wide, .narrow { grid-column: span 12; }
  .hero { padding-right: 1.4rem; }
  .hero-top { flex-direction: column; }
  .readout-grid { grid-template-columns: repeat(4, 1fr); }
}

@media (max-width: 780px) {
  .shell { width: min(1480px, calc(100% - 1rem)); }
  .inquiry-grid { grid-template-columns: 1fr; }
  .readout-grid { grid-template-columns: repeat(2, 1fr); }
  .energy-readout-grid { grid-template-columns: 1fr; }
  .graph-pair { grid-template-columns: 1fr; }
  .theory-columns { grid-template-columns: 1fr; }
  .hero { padding: 1rem 1rem 1.1rem; }
  .hero h1 { font-size: clamp(1.7rem, 10vw, 2.8rem); }
  .range-row { grid-template-columns: 1fr 4rem; }
  .app-layout > [style*="span 6"] { grid-column: span 12; }
}