:root {
    --primary-color: #3498db;
    --secondary-color: #2980b9;
    --background-color: #f5f5f5;
    --display-color: #ffffff;
    --text-color: #333333;
    --button-color: #e0e0e0;
    --button-hover: #d0d0d0;
    --operator-color: #f39c12;
    --operator-hover: #e67e22;
    --equals-color: #2ecc71;
    --equals-hover: #27ae60;
    --function-color: #95a5a6;
    --function-hover: #7f8c8d;
    --sci-color: #9b59b6;
    --sci-hover: #8e44ad;
    --error-color: #e74c3c;
    --border-radius: 8px;
    --box-shadow: 0 4px 8px rgba(0, 0, 0, 0.1);
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

body {
    background-color: var(--background-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    transition: background-color 0.3s, color 0.3s;
}

.calculator {
    width: 320px;
    background-color: var(--background-color);
    border-radius: var(--border-radius);
    box-shadow: var(--box-shadow);
    padding: 20px;
    transition: background-color 0.3s;
}

.display-container {
    background-color: var(--display-color);
    border-radius: var(--border-radius);
    padding: 15px;
    margin-bottom: 15px;
    text-align: right;
    min-height: 80px;
    display: flex;
    flex-direction: column;
    justify-content: space-between;
    word-break: break-all;
}

.history-display {
    font-size: 0.9rem;
    color: #777;
    min-height: 18px;
}

.main-display {
    font-size: 2rem;
    font-weight: bold;
}

.memory-indicator {
    font-size: 0.8rem;
    color: var(--primary-color);
    min-height: 16px;
}

.keypad {
    display: grid;
    grid-template-rows: auto auto auto;
    gap: 10px;
}

.function-buttons, .scientific-buttons, .main-buttons {
    display: grid;
    gap: 8px;
}

.function-buttons {
    grid-template-columns: repeat(6, 1fr);
}

.scientific-buttons {
    grid-template-columns: repeat(4, 1fr);
}

.main-buttons {
    grid-template-columns: repeat(4, 1fr);
}

.btn {
    border: none;
    border-radius: var(--border-radius);
    padding: 15px 0;
    font-size: 1.1rem;
    cursor: pointer;
    transition: all 0.2s;
    background-color: var(--button-color);
    color: var(--text-color);
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.btn-number {
    background-color: var(--button-color);
}

.btn-number:hover {
    background-color: var(--button-hover);
}

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

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

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

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

.btn-function {
    background-color: var(--function-color);
    color: white;
    font-size: 0.9rem;
    padding: 10px 0;
}

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

.btn-sci {
    background-color: var(--sci-color);
    color: white;
    font-size: 0.9rem;
    padding: 10px 0;
}

.btn-sci:hover {
    background-color: var(--sci-hover);
}

.theme-switcher {
    display: flex;
    justify-content: space-between;
    margin-top: 15px;
}

.btn-theme {
    padding: 8px 12px;
    border: none;
    border-radius: var(--border-radius);
    cursor: pointer;
    font-size: 0.8rem;
    background-color: var(--button-color);
    transition: all 0.2s;
}

.btn-theme:hover {
    transform: translateY(-2px);
    box-shadow: 0 2px 4px rgba(0, 0, 0, 0.1);
}

.error {
    color: var(--error-color);
}