/* style.css */

/* --- CSS Variables for Theming --- */
:root {
  --primary-font: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
  --background-color: #f4f7f9;
  --card-background-color: #ffffff;
  --text-color-primary: #2c3e50;
  --text-color-secondary: #7f8c8d;
  --accent-color: #3498db;
  --accent-color-light: #a9cce3;
  --border-color: #e0e6ed;
  --border-color-light: #edf2f7;
  --button-bg-color: #ffffff;
  --button-hover-bg-color: #f8f9fa;
  --input-bg-color: #fdfdfe;
  --select-bg-color: #f7f9fb;

  --border-radius-small: 4px;
  --border-radius-medium: 6px;
  --border-radius-large: 8px;

  --transition-speed: 0.2s;
}

/* --- Basic Reset & Body Styles --- */
body {
  margin: 0;
  font-family: var(--primary-font);
  background-color: var(--background-color);
  color: var(--text-color-primary);
  line-height: 1.6;
  display: flex;
  flex-direction: column;
  min-height: 100vh;
}

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

/* --- Header --- */
.app-header {
  background-color: var(--accent-color);
  color: white;
  padding: 25px 20px;
  text-align: center;
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.app-header h1 {
  margin: 0 0 5px 0;
  font-size: 2rem;
  font-weight: 600;
}
.app-header p {
    margin: 0;
    font-size: 1rem;
    opacity: 0.9;
}

/* --- Main Container --- */
.container {
  flex-grow: 1; /* Takes up remaining vertical space */
  padding: 20px;
  width: 100%;
  max-width: 800px; /* Max width for the content area */
  margin: 20px auto; /* Center the container */
}

/* --- Category Selector --- */
.category-selector {
    background-color: var(--card-background-color);
    padding: 15px 20px;
    border-radius: var(--border-radius-medium);
    margin-bottom: 20px;
    box-shadow: 0 2px 5px rgba(0,0,0,0.05);
    display: flex;
    align-items: center;
    gap: 10px;
}
.category-selector label {
    font-weight: 500;
    color: var(--text-color-secondary);
}
.category-selector select {
    padding: 8px 12px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-small);
    font-size: 0.95rem;
    flex-grow: 1; /* Allow select to take available space */
    background-color: var(--select-bg-color);
    cursor: pointer;
}

/* --- Unit Converter Box --- */
.unit-converter {
  background-color: var(--card-background-color);
  padding: 25px 30px;
  border-radius: var(--border-radius-large);
  box-shadow: 0 5px 15px rgba(0, 0, 0, 0.08);
}

.converter-row {
  display: flex;
  align-items: flex-end; /* Align items based on their bottom edge */
  gap: 20px;
  flex-wrap: wrap; /* Allow wrapping on smaller screens */
}

/* --- Input Groups (From/To) --- */
.input-group {
  flex: 1; /* Allow groups to grow */
  min-width: 200px; /* Minimum width before wrapping */
  background-color: var(--input-bg-color);
  border-radius: var(--border-radius-medium);
  padding: 10px 15px;
  border: 1px solid var(--border-color);
  transition: border-color var(--transition-speed) ease, box-shadow var(--transition-speed) ease;
}

.input-group:focus-within { /* Style when any element inside is focused */
  border-color: var(--accent-color);
  box-shadow: 0 0 0 3px var(--accent-color-light);
}

.input-group label {
  display: block;
  font-size: 0.85rem;
  color: var(--text-color-secondary);
  margin-bottom: 5px;
  font-weight: 500;
}

.input-group input[type="number"] {
  width: 100%;
  border: none;
  background-color: transparent;
  font-size: 1.4rem;
  font-weight: 500;
  color: var(--text-color-primary);
  padding: 8px 0;
  outline: none;
  box-sizing: border-box;
  /* Hide spinner buttons on number inputs (optional) */
  -moz-appearance: textfield;
}
.input-group input[type="number"]::-webkit-outer-spin-button,
.input-group input[type="number"]::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}


/* --- Select Dropdown Styling --- */
.select-wrapper {
  position: relative;
  margin-top: 8px;
  background-color: var(--select-bg-color);
  border-radius: var(--border-radius-small);
  border: 1px solid var(--border-color-light);
  overflow: hidden;
}

.select-wrapper::after { /* Custom arrow */
  content: '▼';
  font-size: 0.8rem;
  color: var(--accent-color);
  position: absolute;
  right: 12px;
  top: 50%;
  transform: translateY(-50%);
  pointer-events: none;
}

.input-group select {
  width: 100%;
  padding: 10px 30px 10px 12px; /* Space for custom arrow */
  border: none;
  background-color: transparent;
  font-size: 0.95rem;
  color: var(--text-color-primary);
  appearance: none; /* Remove default browser arrow */
  -webkit-appearance: none;
  -moz-appearance: none;
  cursor: pointer;
  outline: none;
}

/* --- Swap Button --- */
.swap-button {
  background-color: var(--button-bg-color);
  color: var(--accent-color);
  border: 1px solid var(--border-color);
  border-radius: 50%;
  width: 40px;
  height: 40px;
  font-size: 1.2rem;
  cursor: pointer;
  display: flex;
  justify-content: center;
  align-items: center;
  transition: background-color var(--transition-speed) ease, transform var(--transition-speed) ease, box-shadow var(--transition-speed) ease;
  margin-top: 25px; /* Align roughly with input fields */
  align-self: center;
  flex-shrink: 0;
}

.swap-button:hover {
  background-color: var(--button-hover-bg-color);
   box-shadow: 0 2px 5px rgba(0,0,0,0.1);
   transform: translateY(-1px);
}
.swap-button:active {
  transform: translateY(0);
   box-shadow: none;
}

/* --- Conversion Rate Display --- */
.conversion-rate-display {
    margin-top: 15px;
    text-align: center;
    font-size: 0.9rem;
    color: var(--text-color-secondary);
    font-style: italic;
    min-height: 1.2em; /* Prevent layout shift when text appears */
}


/* --- Footer --- */
.app-footer {
  text-align: center;
  padding: 15px;
  font-size: 0.85rem;
  color: var(--text-color-secondary);
  margin-top: auto; /* Push footer to the bottom */
  background-color: var(--background-color);
  border-top: 1px solid var(--border-color);
}

/* --- Responsive Adjustments --- */
@media (max-width: 650px) {
  .converter-row {
    flex-direction: column;
    align-items: stretch;
    gap: 15px;
  }

  .input-group {
    min-width: unset;
  }

  .swap-button {
    order: 1; /* Place it between the two input groups */
    margin: 5px auto;
    transform: rotate(90deg);
  }

  /* Need explicit order for input groups when direction is column */
  .input-group:first-of-type { order: 0; } /* From group */
  .input-group:last-of-type { order: 2; } /* To group */

}