style.css

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

.container {
    width: 100%;
    height: 100vh;
    background: #e3f9ff;
    display: flex;
    align-items: center;
    justify-content: center;
    background-image: url("https://img.freepik.com/premium-vector/pi-day-seamless-pattern-with-mathematical-constants-baked-pie-template-hand-drawn-illustration_2175-12164.jpg");
    background-size: cover;
}

.calculator {
    background: #3a4452;
    padding: 20px;
    border-radius: 20px;
    width: 420px;
    box-sizing: border-box;
}

.display {
    display: flex;
    flex-direction: column;
    border: 2px solid #00A86B;
    border-radius: 10px;
    justify-content: flex-end;
    padding: 10px;
    margin: 20px 0;
    background: #fff;
    color: #333;
    overflow: hidden;
    height: 100px;
    box-sizing: border-box;
}

.previous-content {
    font-size: 16px;
    opacity: 0.7;
    text-align: right;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.current-content {
    font-size: 24px;
    margin-top: 10px;
    text-align: right;
    white-space: nowrap;
    overflow: hidden;
    text-overflow: ellipsis;
}

.buttons {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
}

.calculator input[type="button"] {
    border: none;
    outline: none;
    width: 60px;
    height: 60px;
    border-radius: 10px;
    box-shadow: -8px 8px 10px lightblue;
    background: transparent;
    font-size: 20px;
    color: #fff;
    cursor: pointer;
    margin: 10px;
    transition: background 0.3s;
    box-sizing: border-box;
    resize: none;
}

.calculator input[type="button"]:hover {
    background: #00A86B;
}

input.equal {
    width: 130px;
    background: #00A86B;
    color: #fff;
}

input.operator {
    color: #00A86B;
}