:root {
  --navy: #2c3e50;
  --softgray: #ecf0f1;
  --teal: #1abc9c;
  --gold: #f1c40f;
  --slate: #7f8c8d;
  --coral: #e74c3c;
  --white: #ffffff;
  --gray-100: #f7fafc;
  --gray-200: #edf2f7;
  --gray-300: #e2e8f0;
  --max-width: 1120px;
  --container-pad: 16px;
  --radius: 10px;
  --shadow-sm: 0 6px 18px rgba(0, 0, 0, 0.06);
  --shadow-xs: 0 1px 2px rgba(0, 0, 0, 0.06);
}

* {
  box-sizing: border-box;
}

html,
body {
  height: 100%;
}

body {
  margin: 0;
  font-family: 'Montserrat', system-ui, -apple-system, 'Segoe UI', Roboto, 'Helvetica Neue', Arial;
  color: var(--navy);
  background: linear-gradient(135deg, #ecf0f1 0%, #d6dbdf 100%);
  padding: 16px;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

/* --------------------------------
   Generic buttons
----------------------------------- */
.btn {
  display: inline-block;
  border-radius: 0.375rem;
  text-decoration: none;
  text-align: center;
  transition: all 0.2s;
  cursor: pointer;
  border: 1px solid transparent;
  font-size: 16px;
  font-weight: 600;
  padding: 12px 24px;
  width: auto;
}

.teal-btn {
  background-color: rgba(26, 188, 156, 0.8);
  color: #fff;
}

.teal-btn:hover {
  background-color: rgba(26, 188, 156, 0.7);
  transform: translateY(-2px);
}

.gold-btn {
  background-color: rgba(241, 196, 15, 1);
  color: var(--navy);
  opacity: 0.9;
}

.gold-btn:hover {
  background-color: rgba(241, 196, 15, 0.5);
  transform: translateY(-2px);
}

.coral-btn {
  background-color: rgba(231, 76, 60, 0.8);
  color: #fff;
}

.coral-btn:hover {
  background-color: rgba(231, 76, 60, 0.7);
  transform: translateY(-2px);
}

.navy-btn {
  background-color: rgba(44, 62, 80, 0.8);
  color: #fff;
}

.navy-btn:hover {
  background-color: rgba(44, 62, 80, 0.7);
  transform: translateY(-2px);
}

.teal-btn:active,
.gold-btn:active,
.coral-btn:active,
.navy-btn:active {
  transform: translateY(1px);
  opacity: 0.95;
}

/* --------------------------------
   Layout basics
----------------------------------- */
.container {
  max-width: var(--max-width);
  margin: 0 auto;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  gap: 18px;
  padding: 18px;
}

li {
  line-height: 2;
}

.main-content {
  flex-grow: 1;
  width: 100%;
  margin: 0 auto;
  padding: 2rem 1rem;
}

.content-area {
  background: var(--gray-100);
  border-radius: 10px;
  padding: 20px;
  margin-bottom: 24px;
}

.content-container {
  max-width: 1200px;
  margin: 0 auto;
}

.grid-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.5rem;
}

.cols {
  display: flex;
  flex-direction: column;
  gap: 24px;
}

/* --------------------------------
   Header
----------------------------------- */
.page-header {
  text-align: center;
  color: var(--navy);
  padding: 1rem;
  position: relative;
}

.page-header h1 {
  font-size: 2rem;
  font-weight: 700;
  margin-bottom: 1rem;
}

.header-grid {
  display: grid;
  grid-template-columns: 1fr auto 1fr;
  align-items: center;
  gap: 12px;
  padding: 8px 0;
}

.page-title {
  margin: 0;
  justify-self: center;
  font-size: clamp(1.25rem, 3vw, 2rem);
  font-weight: 700;
  font-family: 'Montserrat', sans-serif;
}

.header-actions {
  justify-self: end;
}

.header-left {
  justify-self: start;
}

/* --------------------------------
   Simulation panel
----------------------------------- */
.simulation-panel {
  background-color: var(--white);
  padding: 1.5rem;
  border-radius: 0.75rem;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
}

.experiment-area {
  position: relative;
  height: clamp(250px, 40vw, 350px);
  border-bottom: 2px solid var(--gray-300);
  margin-bottom: 1.5rem;
}

.block-container {
  position: absolute;
  left: 500px; /* JS will override this; acts as a desktop fallback */
  bottom: 30px;
}

.weights-container {
  display: flex;
  flex-direction: column;
  align-items: center;
}

.block {
  width: 100px;
  height: 60px;
  background-color: #8b4513;
  position: relative;
  border-radius: 5px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
}

.block-hook {
  position: absolute;
  width: 10px;
  height: 20px;
  border-left: 3px solid #333;
  border-bottom: 3px solid #333;
  border-top: 3px solid #333;
  border-radius: 0 0 0 5px;
  left: -10px;
  top: 20px;
}

.string {
  height: 2px;
  background-color: #000;
  position: absolute;
  transform-origin: left center;
}

.newton-meter {
  position: absolute;
  left: 300px; /* JS will override this; acts as a desktop fallback */
  bottom: 40px;
  width: 195px;
  height: 60px;
  background: linear-gradient(to right, #f0f0f0, #e0e0e0);
  border-radius: 10px;
  border: 3px solid #333;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
  overflow: hidden;
  cursor: grab;
  touch-action: none;
}

.newton-meter.dragging {
  cursor: grabbing;
}

.meter-reading {
  position: absolute;
  width: 4px;
  height: 60px;
  background-color: #ff3333;
  top: 10px;
  transition: left 0.1s ease;
}

.meter-scale {
  font-family: 'Montserrat', sans-serif;
  position: absolute;
  bottom: 5px;
  left: 0;
  width: 100%;
  height: 20px;
  display: flex;
  justify-content: space-between;
  padding: 0 10px;
}

.meter-tick {
  position: absolute;
  width: 1px;
  height: 10px;
  background-color: #333;
  bottom: 20px;
}

.meter-tick.major {
  height: 16px;
  width: 2px;
}

.hook {
  position: absolute;
  width: 10px;
  height: 20px;
  border-right: 3px solid #333;
  border-bottom: 3px solid #333;
  border-top: 3px solid #333;
  border-radius: 0 0 5px 0;
  right: -10px;
  top: 30px;
}

.surface {
  position: absolute;
  width: 100%;
  height: 30px;
  bottom: 0;
  border-radius: 5px;
}

.weight {
  width: 80px;
  height: 20px;
  background-color: #555;
  border-radius: 3px;
  margin-bottom: 2px;
}

.button-container {
  display: flex;
  justify-content: center;
  margin-bottom: 1rem;
}

.control-btn {
  padding: 0.5rem 1rem;
  border-radius: 0.5rem;
  border: none;
  font-weight: 500;
  cursor: pointer;
  transition: all 0.2s ease;
  box-shadow: 0 1px 3px rgba(0, 0, 0, 0.1);
}

.control-btn:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.1);
}

.control-btn:active {
  transform: translateY(1px);
}

.reset-btn {
  background-color: var(--slate);
  color: var(--white);
}

.reset-btn:hover {
  background-color: #6c757d;
}

.instructions {
  background-color: var(--softgray);
  padding: 1rem;
  border-radius: 0.5rem;
}

.instructions h3 {
  font-weight: 600;
  margin-bottom: 0.5rem;
}

.instructions ol {
  padding-left: 1.25rem;
}

.instructions li {
  margin-bottom: 0.25rem;
}

/* --------------------------------
   Control panel
----------------------------------- */
.control-panel {
  background-color: var(--white);
  padding: 1.5rem;
  border-radius: 0.75rem;
  box-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
}

.control-section {
  margin-bottom: 1.5rem;
}

.control-section h3 {
  font-weight: 500;
  margin-bottom: 0.5rem;
}

.surface-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 0.75rem;
}

.surface-option {
  background-color: rgba(241, 196, 15, 0.1);
  padding: 0.75rem;
  border: 2px solid transparent;
  border-radius: 0.5rem;
  display: flex;
  flex-direction: column;
  align-items: center;
  cursor: pointer;
  transition: border-color 0.2s;
}

.surface-option:hover {
  border-color: #3b82f6;
}

.surface-option.active {
  border-color: #3b82f6;
}

.surface-preview {
  width: 4rem;
  height: 1.5rem;
  border-radius: 0.25rem;
  margin-bottom: 0.5rem;
}

.surface-wood {
  background: linear-gradient(90deg, #a87b51 0%, #c19a6b 50%, #a87b51 100%);
}

.surface-ice {
  background: linear-gradient(90deg, #a5f4f7 0%, #dcf7f9 50%, #a5f4f7 100%);
}

.surface-carpet {
  background: linear-gradient(90deg, #5a7247 0%, #7a9267 50%, #5a7247 100%);
  background-image: repeating-linear-gradient(
    45deg,
    transparent,
    transparent 10px,
    rgba(0, 0, 0, 0.1) 10px,
    rgba(0, 0, 0, 0.1) 20px
  );
}

.surface-rubber {
  background: linear-gradient(90deg, #444 0%, #666 50%, #444 100%);
}

.mass-info {
  display: flex;
  justify-content: space-between;
  margin-bottom: 0.5rem;
}

.mass-controls {
  display: flex;
  justify-content: space-between;
  align-items: center;
}

.remove-btn {
  background-color: var(--coral);
  color: var(--white);
}

.remove-btn:hover {
  background-color: #d32f2f;
}

.add-btn {
  background-color: var(--teal);
  color: var(--white);
}

.add-btn:hover {
  background-color: #16a085;
}

.measurements {
  background-color: var(--gray-100);
  padding: 1rem;
  border-radius: 0.5rem;
  margin-bottom: 1.5rem;
}

.measurements h3 {
  font-weight: 500;
  margin-bottom: 0.5rem;
}

.measurement-grid {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 1rem;
}

.measurement-label {
  font-size: 0.875rem;
  color: var(--slate);
}

.measurement-value {
  font-size: 1.25rem;
  font-weight: 700;
}

.kinetic-value {
  color: #3b82f6;
}

.kinetic-value.highlight {
  color: #ff3333;
  transform: scale(1.05);
}

/* --------------------------------
   Data table
----------------------------------- */
.data-section h3 {
  font-weight: 500;
  margin-bottom: 0.5rem;
}

.table-container {
  overflow-x: auto;
}

.data-table {
  width: 100%;
  border-collapse: collapse;
}

.data-table th,
.data-table td {
  border: 1px solid var(--gray-300);
  padding: 0.5rem 0.75rem;
  text-align: left;
}

.data-table th {
  background-color: var(--gray-100);
  font-weight: 500;
}

.record-btn-container {
  display: flex;
  justify-content: flex-end;
  gap: 0.75rem;
  margin-top: 0.75rem;
}

.record-btn {
  background-color: var(--teal);
  color: var(--white);
}

.record-btn:hover {
  background-color: #16a085;
}

/* New clear button style */
.clear-btn {
  background-color: var(--coral);
  color: var(--white);
}

.clear-btn:hover {
  background-color: #d32f2f;
}

/* --------------------------------
   Toast notification
----------------------------------- */
.toast {
  position: fixed;
  top: 20px;
  right: 20px;
  padding: 12px 20px;
  background-color: #4caf50;
  color: white;
  border-radius: 8px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.2);
  opacity: 0;
  transition: opacity 0.3s ease;
  z-index: 1000;
}

.toast.show {
  opacity: 1;
}

/* Initialization guard */
.initialized {
  display: none;
}

/* --------------------------------
   Desktop / tablet breakpoints
----------------------------------- */
@media (min-width: 768px) {
  .grid-layout {
    grid-template-columns: 2fr 1fr;
  }
}

/* --------------------------------
   Mobile adjustments
----------------------------------- */
@media (max-width: 767px) {
  .container {
    padding: 12px;
    gap: 16px;
  }

  .content-area {
    padding: 16px;
    margin-bottom: 16px;
  }

  .simulation-panel,
  .control-panel {
    padding: 16px;
  }

  .page-title {
    font-size: 1.5rem;
  }

  .header-grid {
    grid-template-columns: 1fr;
    grid-auto-flow: row;
    text-align: left;
  }

  .page-title {
    justify-self: start;
  }

  .header-actions {
    justify-self: start;
    width: 100%;
    margin-top: 8px;
  }

  .quiz-btn {
    width: 100%;
    max-width: 420px;
  }

  .experiment-area {
    height: clamp(200px, 35vw, 250px);
    margin-bottom: 1rem;
  }

  /* Only sizing, JS handles horizontal positions */
  .newton-meter {
    width: 160px;
    height: 50px;
  }

  .meter-reading {
    height: 50px;
    top: 5px;
  }

  .meter-tick {
    bottom: 15px;
  }

  .meter-scale {
    font-size: 0.8rem;
    bottom: 2px;
  }

  .block {
    width: 80px;
    height: 50px;
  }

  .surface-grid {
    grid-template-columns: 1fr;
    gap: 0.5rem;
  }

  .surface-option {
    padding: 0.5rem;
    flex-direction: row;
    justify-content: flex-start;
    gap: 12px;
  }

  .surface-preview {
    width: 3rem;
    height: 1.25rem;
    margin-bottom: 0;
  }

  .mass-controls {
    flex-direction: column;
    gap: 8px;
  }

  .measurement-grid {
    grid-template-columns: 1fr;
    gap: 0.75rem;
  }

  .record-btn-container {
    justify-content: center;
    flex-direction: column;
  }

  .record-btn-container .control-btn {
    width: 100%;
    max-width: 220px;
    align-self: center;
  }

  .instructions {
    font-size: 0.9rem;
  }

  .instructions ol {
    padding-left: 1rem;
  }

  .table-container {
    font-size: 0.85rem;
  }

  .data-table th,
  .data-table td {
    padding: 0.375rem 0.5rem;
  }
}