:root {
  --primary-color: #4a55a2;
  --secondary-color: #7895cb;
  --accent-color: #a0bfe0;
  --background-color: #f5f5f5;
  --text-color: #333;
  --button-color: #fff;
  --button-hover: #e6e6e6;
  --button-active: #d9d9d9;
  --operator-color: #7895cb;
  --operator-hover: #6a85b8;
  --operator-active: #5a75a8;
  --equals-color: #4a55a2;
  --equals-hover: #3a4592;
  --equals-active: #2a3582;
  --clear-color: #ff6b6b;
  --clear-hover: #ff5b5b;
  --clear-active: #ff4b4b;
  --display-background: #fff;
  --history-background: #fff;
  --shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
  --border-radius: 10px;
  --transition: all 0.3s ease;
  
  font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
  font-size: 16px;
  line-height: 1.5;
}

body.dark-theme {
  --primary-color: #7895cb;
  --secondary-color: #4a55a2;
  --accent-color: #a0bfe0;
  --background-color: #1a1a1a;
  --text-color: #f5f5f5;
  --button-color: #333;
  --button-hover: #444;
  --button-active: #555;
  --operator-color: #4a55a2;
  --operator-hover: #5a65b2;
  --operator-active: #6a75c2;
  --equals-color: #7895cb;
  --equals-hover: #8aa5db;
  --equals-active: #9ab5eb;
  --clear-color: #ff6b6b;
  --clear-hover: #ff5b5b;
  --clear-active: #ff4b4b;
  --display-background: #333;
  --history-background: #333;
  --shadow: 0 4px 8px rgba(0, 0, 0, 0.3);
}

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

body {
  background-color: var(--background-color);
  color: var(--text-color);
  transition: var(--transition);
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  padding: 20px;
}

#app {
  width: 100%;
  max-width: 1200px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 20px;
}

.calculator-container {
  display: flex;
  flex-direction: column;
  width: 100%;
  max-width: 1200px;
  gap: 20px;
}

@media (min-width: 992px) {
  .calculator-container {
    flex-direction: row;
  }
}

.calculator {
  background-color: var(--background-color);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow);
  padding: 20px;
  width: 100%;
  max-width: 400px;
  margin: 0 auto;
  transition: var(--transition);
}

.calculator-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

.calculator-title {
  font-size: 1.5rem;
  font-weight: 600;
}

.theme-toggle {
  background: none;
  border: none;
  cursor: pointer;
  font-size: 1.5rem;
  color: var(--text-color);
  transition: var(--transition);
}

.display {
  background-color: var(--display-background);
  border-radius: var(--border-radius);
  padding: 15px;
  margin-bottom: 20px;
  box-shadow: inset 0 2px 5px rgba(0, 0, 0, 0.1);
  transition: var(--transition);
}

.expression {
  font-size: 1.2rem;
  min-height: 1.5rem;
  text-align: right;
  color: var(--text-color);
  opacity: 0.7;
  margin-bottom: 5px;
  overflow-x: auto;
  white-space: nowrap;
}

.result {
  font-size: 2rem;
  font-weight: 600;
  text-align: right;
  min-height: 2.5rem;
  overflow-x: auto;
  white-space: nowrap;
}

.keypad {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  grid-template-rows: repeat(7, 1fr);
  gap: 10px;
}

.key {
  background-color: var(--button-color);
  color: var(--text-color);
  border: none;
  border-radius: var(--border-radius);
  padding: 15px 10px;
  font-size: 1.1rem;
  cursor: pointer;
  transition: var(--transition);
  box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.key:hover {
  background-color: var(--button-hover);
  transform: translateY(-2px);
}

.key:active {
  background-color: var(--button-active);
  transform: translateY(0);
}

.key.operator {
  background-color: var(--operator-color);
  color: white;
}

.key.operator:hover {
  background-color: var(--operator-hover);
}

.key.operator:active {
  background-color: var(--operator-active);
}

.key.equals {
  background-color: var(--equals-color);
  color: white;
}

.key.equals:hover {
  background-color: var(--equals-hover);
}

.key.equals:active {
  background-color: var(--equals-active);
}

.key.clear {
  background-color: var(--clear-color);
  color: white;
}

.key.clear:hover {
  background-color: var(--clear-hover);
}

.key.clear:active {
  background-color: var(--clear-active);
}

.key.function {
  background-color: var(--secondary-color);
  color: white;
  font-size: 0.9rem;
}

.key.function:hover {
  background-color: var(--operator-hover);
}

.key.function:active {
  background-color: var(--operator-active);
}

.history-container {
  background-color: var(--history-background);
  border-radius: var(--border-radius);
  box-shadow: var(--shadow);
  padding: 20px;
  width: 100%;
  max-width: 400px;
  margin: 0 auto;
  transition: var(--transition);
  display: flex;
  flex-direction: column;
}

.history-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
}

.history-title {
  font-size: 1.5rem;
  font-weight: 600;
}

.clear-history {
  background-color: var(--clear-color);
  color: white;
  border: none;
  border-radius: var(--border-radius);
  padding: 5px 10px;
  font-size: 0.9rem;
  cursor: pointer;
  transition: var(--transition);
}

.clear-history:hover {
  background-color: var(--clear-hover);
}

.clear-history:active {
  background-color: var(--clear-active);
}

.history-list {
  overflow-y: auto;
  max-height: 400px;
  flex-grow: 1;
}

.history-item {
  padding: 10px;
  border-bottom: 1px solid rgba(0, 0, 0, 0.1);
  cursor: pointer;
  transition: var(--transition);
}

.history-item:hover {
  background-color: rgba(0, 0, 0, 0.05);
}

.history-expression {
  font-size: 1rem;
  color: var(--text-color);
  opacity: 0.7;
}

.history-result {
  font-size: 1.2rem;
  font-weight: 600;
}

.empty-history {
  text-align: center;
  padding: 20px;
  color: var(--text-color);
  opacity: 0.5;
}

@media (max-width: 480px) {
  .calculator, .history-container {
    padding: 15px;
  }
  
  .key {
    padding: 10px 5px;
    font-size: 0.9rem;
  }
  
  .key.function {
    font-size: 0.8rem;
  }
  
  .result {
    font-size: 1.5rem;
  }
  
  .expression {
    font-size: 1rem;
  }
}