:root {
    --bg-color: #2c2c2c;
    --btn-bg: #3a3a3a;
    --btn-color: #ffffff;
    --accent-color: #ff9f43;
    --operator-color: #54a0ff;
    --clear-color: #ee5253;
}

body {
    background-color: var(--bg-color);
    color: white;
    font-family: 'Segoe UI', sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
}

.calculator {
    width: 320px;
    background-color: var(--btn-bg);
    border-radius: 20px;
    box-shadow: 0 10px 25px rgba(0, 0, 0, 0.5);
    padding: 20px;
}

.display {
    background-color: #222;
    color: #fff;
    font-size: 2.5rem;
    text-align: right;
    padding: 20px;
    border-radius: 10px;
    margin-bottom: 20px;
    height: 60px;
    overflow: hidden;
    white-space: nowrap;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

button {
    padding: 20px;
    font-size: 1.2rem;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    background-color: #444;
    color: white;
    transition: transform 0.1s, background-color 0.2s;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.2);
}

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

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

.btn-equals {
    background-color: var(--accent-color);
    grid-column: span 2;
}

.btn-clear {
    background-color: var(--clear-color);
    grid-column: span 2;
}

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