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

:root {
  --bg-color: #2c2c2c;
  --calculator-bg: #1a1a1a;
  --calculator-border: #555;
  --text-color: #e0e0e0;
  --input-bg: #333;
  --input-border: #666;
  --input-focus-bg: #444;
  --output-bg: #222;
  --button-bg: #444;
  --button-border: #666;
  --button-hover: #555;
  --evaluate-bg: #2a5aa0;
  --evaluate-border: #1e4a87;
  --evaluate-hover: #1e4a87;
  --extra-bg: #3a3a3a;
  --extra-text: #ccc;
  --extra-hover: #4a4a4a;
  --scientific-bg: #4a5a5a;
  --scientific-border: #3a4a4a;
  --scientific-hover: #3a4a4a;
  --numbers-bg: #2a2a2a;
  --numbers-hover: #3a3a3a;
  --operators-bg: #8b6914;
  --operators-border: #6b5010;
  --operators-hover: #6b5010;
  --shadow: rgba(0, 0, 0, 0.4);
}

body.light-mode {
  --bg-color: #f0f0f0;
  --calculator-bg: #ffffff;
  --calculator-border: #ccc;
  --text-color: #333;
  --input-bg: #fff;
  --input-border: #999;
  --input-focus-bg: #fff;
  --output-bg: #f8f8f8;
  --button-bg: #e8e8e8;
  --button-border: #bbb;
  --button-hover: #d8d8d8;
  --evaluate-bg: #4a90e2;
  --evaluate-border: #357abd;
  --evaluate-hover: #357abd;
  --extra-bg: #f5f5f5;
  --extra-text: #555;
  --extra-hover: #eaeaea;
  --scientific-bg: #6c7b7f;
  --scientific-border: #5a6569;
  --scientific-hover: #5a6569;
  --numbers-bg: #ffffff;
  --numbers-hover: #f0f0f0;
  --operators-bg: #d4a574;
  --operators-border: #b8935f;
  --operators-hover: #b8935f;
  --shadow: rgba(0, 0, 0, 0.1);
}

body {
  font-family: Arial, sans-serif;
  background: var(--bg-color);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px;
  transition: background-color 0.3s ease;
}

.calculator {
  background: var(--calculator-bg);
  border: 2px solid var(--calculator-border);
  border-radius: 8px;
  padding: 20px;
  box-shadow: 0 6px 12px var(--shadow);
  width: 100%;
  max-width: 400px;
  transition: all 0.3s ease;
}

.header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 15px;
}

h1 {
  color: var(--text-color);
  text-align: center;
  font-size: 1.4rem;
  font-weight: normal;
  flex: 1;
}

.theme-toggle {
  padding: 8px 12px;
  background: var(--button-bg);
  color: var(--text-color);
  border: 1px solid var(--button-border);
  border-radius: 4px;
  font-size: 1.2rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.theme-toggle:hover {
  background: var(--button-hover);
}

.display {
  margin-bottom: 15px;
}

#input-value {
  width: 100%;
  padding: 12px;
  font-size: 1rem;
  border: 1px solid var(--input-border);
  border-radius: 4px;
  background: var(--input-bg);
  color: var(--text-color);
  margin-bottom: 8px;
  font-family: monospace;
  transition: all 0.3s ease;
}

#input-value:focus {
  outline: none;
  border-color: #888;
  background: var(--input-focus-bg);
}

#output {
  background: var(--output-bg);
  color: var(--text-color);
  padding: 10px 12px;
  border: 1px solid var(--calculator-border);
  border-radius: 4px;
  font-weight: normal;
  font-size: 0.95rem;
  font-family: monospace;
  min-height: 18px;
  transition: all 0.3s ease;
}

.main-controls {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 6px;
  margin-bottom: 12px;
}

.main-controls button {
  padding: 10px;
  background: var(--button-bg);
  color: var(--text-color);
  border: 1px solid var(--button-border);
  border-radius: 4px;
  font-size: 0.95rem;
  font-weight: normal;
  cursor: pointer;
  transition: all 0.3s ease;
}

.main-controls button:hover {
  background: var(--button-hover);
}

#evaluate {
  background: var(--evaluate-bg);
  color: white;
  border-color: var(--evaluate-border);
}

#evaluate:hover {
  background: var(--evaluate-hover);
}

.extra-controls {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 6px;
  margin-bottom: 12px;
}

.extra-controls button {
  padding: 8px;
  background: var(--extra-bg);
  color: var(--extra-text);
  border: 1px solid var(--calculator-border);
  border-radius: 4px;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.extra-controls button:hover {
  background: var(--extra-hover);
}

.button-panels {
  display: grid;
  grid-template-columns: 1fr 2fr;
  gap: 12px;
}

.left-panel {
  display: grid;
  grid-template-columns: repeat(2, 1fr);
  gap: 6px;
}

.left-panel button {
  padding: 10px 6px;
  background: var(--scientific-bg);
  color: white;
  border: 1px solid var(--scientific-border);
  border-radius: 4px;
  font-size: 0.85rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.left-panel button:hover {
  background: var(--scientific-hover);
}

.right-panel {
  display: flex;
  flex-direction: column;
  gap: 8px;
}

.numbers {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 6px;
}

.numbers button {
  padding: 12px;
  background: var(--numbers-bg);
  color: var(--text-color);
  border: 1px solid var(--calculator-border);
  border-radius: 4px;
  font-size: 1rem;
  font-weight: normal;
  cursor: pointer;
  transition: all 0.3s ease;
}

.numbers button:hover {
  background: var(--numbers-hover);
}

.operators {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 6px;
}

.operators button {
  padding: 10px;
  background: var(--operators-bg);
  color: white;
  border: 1px solid var(--operators-border);
  border-radius: 4px;
  font-size: 1rem;
  cursor: pointer;
  transition: all 0.3s ease;
}

.operators button:hover {
  background: var(--operators-hover);
}

@media (max-width: 480px) {
  .calculator {
    padding: 15px;
    margin: 10px;
  }

  h1 {
    font-size: 1.2rem;
  }

  .button-panels {
    grid-template-columns: 1fr;
    gap: 8px;
  }

  .left-panel {
    grid-template-columns: repeat(3, 1fr);
    order: 2;
  }
}

button:active {
  background: var(--button-hover);
}

button:focus {
  outline: 1px solid var(--evaluate-bg);
}