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

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #f3f4f6;
}

.calculator {
    background-color: #22252d;
    border-radius: 20px;
    box-shadow: 0px 10px 30px rgba(0, 0, 0, 0.2);
    width: 320px;
    overflow: hidden;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    padding: 20px;
    gap: 10px;
}

.display {
    grid-column: 1 / -1;
    background-color: #22252d;
    display: flex;
    flex-direction: column;
    align-items: flex-end;
    justify-content: space-around;
    padding: 20px 10px;
    word-wrap: break-word;
    word-break: break-all;
    height: 100px;
    border-bottom: 2px solid #292d36;
    margin-bottom: 10px;
}

.previous-operand {
    color: #a5a5a5;
    font-size: 1.2rem;
}

.current-operand {
    color: white;
    font-size: 2.5rem;
    font-weight: bold;
}

.btn {
    cursor: pointer;
    border: none;
    outline: none;
    background-color: #292d36;
    color: white;
    font-size: 1.5rem;
    padding: 15px;
    border-radius: 10px;
    transition: background-color 0.2s;
}

.btn:hover {
    background-color: #3f4451;
}

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

.operator {
    color: #26e7a6;
    background-color: #2b303b;
}

.clear, .delete {
    color: #ff6b6b;
    background-color: #2b303b;
}

.equal {
    background-color: #26e7a6;
    color: #22252d;
    font-weight: bold;
}

.equal:hover {
    background-color: #20c48d;
}