:root {
    --primary-color: #2c3e50;
    --secondary-color: #34495e;
    --accent-color: #f09610;
    --text-color: #ecf0f1;
    --display-color: #1a252f;
    --button-hover: #f09610;
}

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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #29333d;
}

.calculator {
    width: 100%;
    max-width: 340px;
    border-radius: 12px;
    overflow: hidden;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
    background-color: var(--primary-color);
}

.display {
    padding: 20px;
    text-align: right;
    background-color: var(--display-color);
    color: var(--text-color);
    position: relative;
}

.previous-operand {
    min-height: 24px;
    font-size: 16px;
    opacity: 0.7;
    word-wrap: break-word;
}

.current-operand {
    min-height: 40px;
    font-size: 32px;
    font-weight: 500;
    margin-top: 8px;
    word-wrap: break-word;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(5, 1fr);
    gap: 1px;
    background-color: var(--secondary-color);
}

button {
    border: none;
    outline: none;
    padding: 18px 10px;
    font-size: 18px;
    cursor: pointer;
    background-color: var(--primary-color);
    color: var(--text-color);
    transition: all 0.2s;
    position: relative;
}

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

button:active {
    transform: scale(0.95);
}

.span-2 {
    grid-column: span 2;
}

.operation {
    background-color: var(--secondary-color);
}

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

.scientific {
    font-size: 14px;
}

@media (max-width: 400px) {
    button {
        padding: 16px 8px;
        font-size: 16px;
    }
    
    .scientific {
        font-size: 12px;
    }
}