:root {
  --bt-teal: #03504e;
  --bt-teal-soft: #0b6d6a;
  --bt-bg: #f8f8f6;
  --bt-panel: #ffffff;
  --bt-text: #1e1e1e;
  --bt-muted: #777777;
  --bt-border: #dddddd;
  --bt-radius: 12px;
  --bt-shadow: 0 6px 16px rgba(0, 0, 0, 0.06);
}

*,
*::before,
*::after {
  box-sizing: border-box;
}

html,
body {
  margin: 0;
  padding: 0;
  font-family: system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI",
    sans-serif;
  background: var(--bt-bg);
  color: var(--bt-text);
}

/* Header */

.bt-header {
  background: var(--bt-teal);
  color: #ffffff;
  padding: 1.25rem 1rem;
}

.bt-header-inner {
  max-width: 900px;
  margin: 0 auto;
}

.bt-logo {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  opacity: 0.8;
}

.bt-header h1 {
  margin: 0.25rem 0 0.2rem;
  font-size: 1.6rem;
}

.bt-tagline {
  margin: 0;
  font-size: 0.95rem;
  opacity: 0.9;
}

/* Layout */

.bt-main {
  max-width: 900px;
  margin: 0 auto;
  padding: 1rem;
}

.bt-panel {
  background: var(--bt-panel);
  border-radius: var(--bt-radius);
  box-shadow: var(--bt-shadow);
  padding: 1rem 1.1rem 1.25rem;
  margin-bottom: 1rem;
}

.bt-panel h2 {
  margin-top: 0;
  font-size: 1.1rem;
}

.bt-help,
.bt-notan-info {
  font-size: 0.9rem;
  color: var(--bt-muted);
  margin-top: 0.35rem;
}

/* File input */

.bt-file-label {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  margin-top: 0.75rem;
  padding: 0.6rem 1rem;
  border-radius: 999px;
  border: 1px dashed var(--bt-teal-soft);
  color: var(--bt-teal);
  font-size: 0.9rem;
  cursor: pointer;
  background: rgba(3, 80, 78, 0.06);
}

.bt-file-label input {
  display: none;
}

/* Buttons */

.bt-button {
  border: none;
  border-radius: 999px;
  padding: 0.6rem 1.2rem;
  font-size: 0.9rem;
  cursor: pointer;
  background: var(--bt-teal);
  color: #ffffff;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.3rem;
}

.bt-button:hover {
  background: var(--bt-teal-soft);
}

.bt-button:disabled {
  opacity: 0.5;
  cursor: default;
}

.bt-button-ghost {
  background: transparent;
  border: 1px solid var(--bt-border);
  color: var(--bt-muted);
}

.bt-button-ghost:hover {
  border-color: var(--bt-teal);
  color: var(--bt-teal);
}

.bt-button-secondary {
  background: #ffffff;
  color: var(--bt-teal);
  border: 1px solid var(--bt-teal-soft);
}

.bt-button-secondary:hover {
  background: rgba(3, 80, 78, 0.06);
}

.bt-actions-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.6rem;
  margin-top: 0.9rem;
}

/* Controls */

.bt-controls-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.75rem;
  margin-top: 0.75rem;
  font-size: 0.9rem;
}

#threshold-range {
  flex: 1;
}

#threshold-value {
  font-weight: 600;
  margin-left: 0.25rem;
}

.bt-toggle-label {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}

.bt-select {
  padding: 0.3rem 0.7rem;
  border-radius: 999px;
  border: 1px solid var(--bt-border);
  font-size: 0.9rem;
  background: #ffffff;
}

/* Tone colour controls */

.bt-tone-colors {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
  margin-top: 0.75rem;
}

.bt-tone-color {
  font-size: 0.8rem;
  color: var(--bt-muted);
}

.bt-tone-color label {
  display: inline-flex;
  align-items: center;
  gap: 0.4rem;
}

.bt-tone-color input[type="color"] {
  width: 36px;
  height: 24px;
  border-radius: 6px;
  border: 1px solid var(--bt-border);
  padding: 0;
  background: transparent;
  cursor: pointer;
}

.bt-tone-hidden {
  display: none;
}

/* Canvas */

.bt-canvas-wrapper {
  position: relative;
  width: 100%;
  max-width: 100%;
  border-radius: var(--bt-radius);
  border: 1px solid var(--bt-border);
  overflow: hidden;
  background: #f0f0f0;
}

#notan-canvas {
  display: block;
  width: 100%;
  height: auto;
  background: #f0f0f0;
}

.bt-placeholder {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  color: var(--bt-muted);
  font-size: 0.9rem;
  text-align: center;
  padding: 1rem;
}

/* Guide */

.bt-guide-panel {
  transition: opacity 0.25s ease, transform 0.25s ease;
}

.bt-guide-panel-hidden {
  opacity: 0;
  pointer-events: none;
  transform: translateY(6px);
}

.bt-guide-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 0.5rem;
}

.bt-guide-step {
  font-size: 0.8rem;
  padding: 0.25rem 0.7rem;
  border-radius: 999px;
  border: 1px solid var(--bt-border);
  color: var(--bt-muted);
}

.bt-guide-text {
  font-size: 0.9rem;
  margin: 0.75rem 0 0.25rem;
}

/* Footer */

.bt-footer {
  padding: 1rem;
  text-align: center;
  font-size: 0.8rem;
  color: var(--bt-muted);
}

/* Responsive */

@media (min-width: 720px) {
  .bt-main {
    padding: 1.25rem 1rem 1.5rem;
  }

  .bt-panel {
    padding: 1.25rem 1.5rem 1.5rem;
  }
}