:root {
  --color-bg: #0f0f0f;
  --color-surface: #1a1a1a;
  --color-text: #e8e8e8;
  --color-text-light: #777;
  --color-accent: #3ecfff;
  --color-accent-glow: rgba(62, 207, 255, 0.25);
  --color-error: #ff5252;
  --color-border: #2a2a2a;
  --radius: 8px;
  --shadow: 0 2px 12px rgba(0, 0, 0, 0.4);
  --font-stack: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
}

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: var(--font-stack);
  color: var(--color-text);
  background: var(--color-bg);
  line-height: 1.6;
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  align-items: center;
}

header {
  text-align: center;
  padding: 2rem 1rem 0.5rem;
  width: 100%;
}

header h1 {
  font-size: 1.25rem;
  color: var(--color-text-light);
  font-weight: 700;
  letter-spacing: -0.02em;
}

.subtitle {
  font-size: 0.8rem;
  color: var(--color-text-light);
  margin-top: 0.15rem;
}

main {
  width: 100%;
  max-width: 480px;
  padding: 1rem;
  flex: 1;
  display: flex;
  flex-direction: column;
  gap: 1.5rem;
}

/* Rate info — secondary */
.rate-info {
  text-align: center;
  padding: 0.5rem 0;
}

.rate-label {
  display: block;
  font-size: 0.85rem;
  color: var(--color-text-light);
  text-transform: uppercase;
  letter-spacing: 0.08em;
}

.rate-value {
  display: inline;
  font-size: 1.25rem;
  font-weight: 800;
  color: var(--color-text);
  font-variant-numeric: tabular-nums;
  line-height: 1.3;
}

.rate-currency {
  display: inline;
  font-size: 0.85rem;
  color: var(--color-text-light);
  margin-left: 0.15rem;
}

.rate-timestamp {
  font-size: 0.75rem;
  color: var(--color-text-light);
  margin-top: 0.25rem;
}

.retry-btn {
  display: none;
  margin-top: 0.5rem;
  padding: 0.4rem 1rem;
  border: 1px solid var(--color-accent);
  border-radius: var(--radius);
  background: transparent;
  color: var(--color-accent);
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s, color 0.15s;
}

.retry-btn:hover {
  background: var(--color-accent);
  color: var(--color-bg);
}

.rate-info.error .rate-value {
  color: var(--color-error);
  font-size: 0.95rem;
  font-weight: 600;
}

.rate-info.error .rate-currency {
  display: none;
}

.rate-info.error .retry-btn {
  display: inline-block;
}

.rate-info.loading .rate-value {
  font-size: 0;
}

.rate-info.loading .rate-value::after {
  content: "";
  display: inline-block;
  width: 1.25rem;
  height: 1.25rem;
  border: 2.5px solid var(--color-border);
  border-top-color: var(--color-accent);
  border-radius: 50%;
  animation: spin 0.6s linear infinite;
  vertical-align: middle;
}

.rate-info.loading .rate-currency {
  display: none;
}

@keyframes spin {
  to { transform: rotate(360deg); }
}

/* Slider converter — hero */
.slider-converter {
  text-align: center;
  padding: 1.5rem 0;
}

.slider-converter h2 {
  display: none;
}

.slider-row {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  margin-bottom: 1.5rem;
}

.slider-row input[type="range"] {
  flex: 1;
  -webkit-appearance: none;
  appearance: none;
  height: 4px;
  background: var(--color-border);
  border-radius: 2px;
  outline: none;
}

.slider-row input[type="range"]::-webkit-slider-thumb {
  -webkit-appearance: none;
  appearance: none;
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--color-accent);
  cursor: pointer;
  border: none;
  box-shadow: 0 0 12px var(--color-accent-glow);
  transition: box-shadow 0.15s;
}

.slider-row input[type="range"]::-webkit-slider-thumb:hover {
  box-shadow: 0 0 20px var(--color-accent-glow);
}

.slider-row input[type="range"]::-moz-range-thumb {
  width: 24px;
  height: 24px;
  border-radius: 50%;
  background: var(--color-accent);
  cursor: pointer;
  border: none;
  box-shadow: 0 0 12px var(--color-accent-glow);
}

.slider-row input[type="range"]::-moz-range-track {
  height: 4px;
  background: var(--color-border);
  border-radius: 2px;
}

/* Hero values — stacked, same size */
.hero-value {
  font-size: 3rem;
  font-weight: 800;
  color: var(--color-accent);
  font-variant-numeric: tabular-nums;
  line-height: 1.2;
  text-shadow: 0 0 30px var(--color-accent-glow);
  will-change: transform;
}

.hero-label {
  font-size: 0.9rem;
  color: var(--color-text-light);
  font-weight: 600;
  letter-spacing: 0.05em;
}

.hero-block {
  margin-bottom: 0.5rem;
}

.hero-block:last-child {
  margin-bottom: 0;
}

/* Bounce animation */
@keyframes bounce {
  0%   { transform: scale(1); }
  40%  { transform: scale(1.08); }
  100% { transform: scale(1); }
}

.hero-value.bouncing {
  animation: bounce 200ms cubic-bezier(0.34, 1.56, 0.64, 1);
}

/* Footer */
footer {
  text-align: center;
  padding: 1rem;
  font-size: 0.75rem;
  color: var(--color-text-light);
  width: 100%;
}

/* Tablet */
@media (min-width: 768px) {
  header h1 {
    font-size: 1.4rem;
  }

  main {
    max-width: 560px;
    padding: 1.5rem;
  }

  .hero-value {
    font-size: 3.5rem;
  }
}

/* Desktop */
@media (min-width: 1024px) {
  main {
    max-width: 620px;
  }

  .hero-value {
    font-size: 4rem;
  }
}