:root {
  --font-family: "Segoe UI", Tahoma, Geneva, Verdana, sans-serif;
  --transition-speed: 0.25s;
}

.theme-light {
  --background: #f3f6fc;
  --surface-color: #ffffff;
  --surface-border: rgba(15, 23, 42, 0.08);
  --surface-shadow: 0 20px 45px rgba(0, 74, 173, 0.12);
  --text-color: #1f2933;
  --muted-text: #52606d;
  --primary-color: #004aad;
  --primary-dark: #002f6c;
  --accent-color: #00b894;
  --error-color: #d64545;
  --input-bg: rgba(255, 255, 255, 0.9);
  --input-border: rgba(0, 74, 173, 0.2);
  --input-focus-ring: rgba(0, 74, 173, 0.2);
  --button-text-color: #ffffff;
  --button-shadow: 0 12px 24px rgba(0, 74, 173, 0.25);
  --button-shadow-hover: 0 16px 32px rgba(0, 74, 173, 0.32);
  --result-meta-color: #52606d;
}

.theme-dark {
  --background: #050b16;
  --surface-color: #0f1b2f;
  --surface-border: rgba(148, 163, 184, 0.12);
  --surface-shadow: 0 25px 55px rgba(3, 10, 24, 0.7);
  --text-color: #e5edff;
  --muted-text: #94a3b8;
  --primary-color: #7aa2ff;
  --primary-dark: #3a7bd5;
  --accent-color: #7df1c0;
  --error-color: #f97070;
  --input-bg: rgba(15, 27, 47, 0.9);
  --input-border: rgba(122, 162, 255, 0.35);
  --input-focus-ring: rgba(122, 162, 255, 0.35);
  --button-text-color: #050b16;
  --button-shadow: 0 12px 30px rgba(58, 123, 213, 0.45);
  --button-shadow-hover: 0 18px 36px rgba(58, 123, 213, 0.55);
  --result-meta-color: #94a3b8;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: var(--font-family);
  background: var(--background);
  color: var(--text-color);
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  padding: 1.5rem;
  transition: background var(--transition-speed) ease,
    color var(--transition-speed) ease;
}

.app {
  background: var(--surface-color);
  max-width: 480px;
  width: 100%;
  border-radius: 16px;
  padding: 2rem;
  border: 1px solid var(--surface-border);
  box-shadow: var(--surface-shadow);
  transition: background var(--transition-speed) ease,
    box-shadow var(--transition-speed) ease,
    border-color var(--transition-speed) ease;
}

.app__header {
  display: flex;
  flex-direction: column;
  gap: 0.75rem;
  align-items: center;
  text-align: center;
  margin-bottom: 1.75rem;
}

.app__title {
  margin: 0 0 0.5rem;
  font-size: 2rem;
  color: var(--primary-color);
}

.app__subtitle {
  margin: 0;
  line-height: 1.5;
  color: var(--muted-text);
}

.pace-form {
  display: grid;
  gap: 1rem;
}

.pace-form__label {
  display: grid;
  gap: 0.35rem;
  font-weight: 600;
  font-size: 0.95rem;
}

.pace-form__input {
  padding: 0.75rem;
  background: var(--input-bg);
  border: 1px solid var(--input-border);
  border-radius: 10px;
  font-size: 1rem;
  color: var(--text-color);
  transition: border-color var(--transition-speed) ease,
    box-shadow var(--transition-speed) ease,
    background var(--transition-speed) ease,
    color var(--transition-speed) ease;
}

.pace-form__input:focus {
  outline: none;
  border-color: var(--primary-color);
  box-shadow: 0 0 0 3px var(--input-focus-ring);
}

.pace-form__input::placeholder {
  color: var(--muted-text);
  opacity: 0.7;
}

.pace-form__button {
  margin-top: 0.5rem;
  padding: 0.85rem 1.25rem;
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--button-text-color);
  background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
  border: none;
  border-radius: 999px;
  cursor: pointer;
  box-shadow: var(--button-shadow);
  transition: transform var(--transition-speed) ease,
    box-shadow var(--transition-speed) ease,
    background var(--transition-speed) ease,
    color var(--transition-speed) ease;
}

.pace-form__button:hover,
.pace-form__button:focus {
  transform: translateY(-1px);
  box-shadow: var(--button-shadow-hover);
}

.pace-result {
  margin-top: 2rem;
  min-height: 3rem;
  display: grid;
  gap: 0.5rem;
}

.distance-guide {
  margin-bottom: 2rem;
  padding: 1.25rem;
  border: 1px solid var(--surface-border);
  border-radius: 12px;
  background: rgba(255, 255, 255, 0.02);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.03);
  display: grid;
  gap: 0.85rem;
}

.distance-guide__header {
  display: flex;
  align-items: center;
  justify-content: center;
}

.theme-light .distance-guide {
  background: rgba(0, 74, 173, 0.04);
  box-shadow: inset 0 1px 0 rgba(255, 255, 255, 0.8);
}

.distance-guide__title {
  margin: 0;
  font-size: 1.1rem;
  color: var(--primary-color);
}

.distance-guide__toggle {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 0.85rem 1.25rem;
  border-radius: 999px;
  border: none;
  background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
  color: var(--button-text-color);
  font-size: 1rem;
  font-weight: 600;
  cursor: pointer;
  box-shadow: var(--button-shadow);
  transition: transform var(--transition-speed) ease,
    box-shadow var(--transition-speed) ease,
    background var(--transition-speed) ease,
    color var(--transition-speed) ease;
}

.distance-guide__toggle:hover,
.distance-guide__toggle:focus {
  transform: translateY(-1px);
  box-shadow: var(--button-shadow-hover);
}

.distance-guide__toggle:focus {
  outline: none;
  box-shadow: 0 0 0 3px var(--input-focus-ring), var(--button-shadow-hover);
}

.distance-guide__description {
  margin: 0;
  color: var(--muted-text);
  font-size: 0.9rem;
}

.distance-guide__content[hidden] {
  display: none;
}

.distance-guide__content {
  display: grid;
  gap: 0.5rem;
}

.distance-guide__table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
}

.distance-guide__table th,
.distance-guide__table td {
  padding: 0.5rem 0.75rem;
  text-align: left;
}

.distance-guide__table thead th {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted-text);
  border-bottom: 1px solid var(--surface-border);
}

.distance-guide__table tbody tr + tr td {
  border-top: 1px solid var(--surface-border);
}

.distance-guide__table tbody tr:hover {
  background: rgba(122, 162, 255, 0.08);
}

.theme-light .distance-guide__table tbody tr:hover {
  background: rgba(0, 74, 173, 0.08);
}

.pace-result__value {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--accent-color);
}

.pace-result__meta {
  margin: 0;
  line-height: 1.5;
  color: var(--result-meta-color);
}

.pace-result__error {
  color: var(--error-color);
  font-weight: 600;
}

.theme-toggle {
  align-self: flex-end;
  padding: 0.35rem 0.9rem;
  border-radius: 999px;
  border: 1px solid rgba(255, 255, 255, 0.18);
  background: rgba(255, 255, 255, 0.08);
  color: var(--text-color);
  font-size: 0.85rem;
  font-weight: 600;
  cursor: pointer;
  transition: background var(--transition-speed) ease,
    color var(--transition-speed) ease,
    border-color var(--transition-speed) ease,
    transform var(--transition-speed) ease;
}

.theme-light .theme-toggle {
  border-color: rgba(0, 74, 173, 0.2);
  background: rgba(0, 74, 173, 0.08);
}

.theme-toggle:hover,
.theme-toggle:focus {
  transform: translateY(-1px);
}

.theme-toggle:focus {
  outline: none;
  box-shadow: 0 0 0 3px var(--input-focus-ring);
}

@media (max-width: 480px) {
  .app {
    padding: 1.5rem;
  }

  .app__title {
    font-size: 1.75rem;
  }
}