:root {
    --bg-color: #121212;
    --calc-bg: #1e1e1e;
    --btn-bg: #2d2d2d;
    --btn-hover: #3d3d3d;
    --text-color: #ffffff;
    --primary-color: #00adb5;
    --operator-color: #ff5722;
    --action-color: #393e46;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins', sans-serif;
}

body {
    background-color: var(--bg-color);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator {
    background-color: var(--calc-bg);
    padding: 20px;
    border-radius: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
    width: 100%;
    max-width: 350px;
}

.display {
    background-color: #000;
    color: var(--text-color);
    text-align: right;
    padding: 20px;
    border-radius: 10px;
    margin-bottom: 20px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    height: 100px;
    word-wrap: break-word;
    word-break: break-all;
}

.previous-operand {
    font-size: 1rem;
    color: rgba(255, 255, 255, 0.6);
    height: 20px;
}

.current-operand {
    font-size: 2.5rem;
    font-weight: 500;
}

.buttons-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.btn {
    background-color: var(--btn-bg);
    border: none;
    color: var(--text-color);
    font-size: 1.2rem;
    padding: 15px;
    border-radius: 50%;
    cursor: pointer;
    transition: all 0.2s ease;
    user-select: none;
}

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

.btn:active {
    transform: scale(0.95);
}

.span-two {
    grid-column: span 2;
    border-radius: 30px;
}

.operator {
    color: var(--primary-color);
    font-weight: bold;
}

.action {
    color: var(--operator-color);
}

.equals {
    background-color: var(--primary-color);
    color: #000;
    font-weight: bold;
}

.equals:hover {
    background-color: #00ddeb;
}