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

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

.container {
    text-align: center;
}

h1 {
    color: #222;
    margin-bottom: 20px;
    font-weight: 400;
    letter-spacing: 1px;
}

/* Calculator Card */
.calculator {
    background-color: #fff;
    padding: 25px;
    border-radius: 20px;
    box-shadow: 0 12px 25px rgba(0,0,0,0.12), 0 6px 12px rgba(0,0,0,0.08);
    width: 320px;
}

/* Display */
#display {
    width: 100%;
    height: 65px;
    font-size: 2rem;
    text-align: right;
    padding: 12px;
    border-radius: 12px;
    border: 1px solid #ddd;
    margin-bottom: 20px;
    background-color: #f9f9f9;
    color: #333;
    box-shadow: inset 0 2px 5px rgba(0,0,0,0.05);
}

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

/* Buttons Style */
button {
    padding: 18px;
    font-size: 1.3rem;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.15s ease;
    box-shadow: 0 4px rgba(0,0,0,0.1);
    color: #fff;
}

/* Number Buttons */
button:not(.operator):not(.equal) {
    background-color: #6c63ff;
}

button:not(.operator):not(.equal):hover {
    background-color: #5b52e6;
}

button:not(.operator):not(.equal):active {
    transform: translateY(2px);
    box-shadow: 0 2px rgba(0,0,0,0.1);
}

/* Operator Buttons */
button.operator {
    background-color: #ff6584;
}

button.operator:hover {
    background-color: #e55576;
}

button.operator:active {
    transform: translateY(2px);
    box-shadow: 0 2px rgba(0,0,0,0.1);
}

/* Equal Button */
button.equal {
    background-color: #00b894;
    grid-row: span 2;
}

button.equal:hover {
    background-color: #009f7f;
}

button.equal:active {
    transform: translateY(2px);
    box-shadow: 0 2px rgba(0,0,0,0.1);
}

/* Zero Button */
button.zero {
    grid-column: span 2;
}