:root {
    --bg: #f8f8f8;
    --screen-bg: #fff;
    --number-bg: #e0e0e0;
    --number-hover: #d5d5d5;
    --operator-bg: #b0b0b0;
    --operator-hover: #999;
    --equal-bg: #4a4a4a;
    --equal-hover: #2e2e2e;
    --clear-bg: #d9534f;
    --clear-hover: #c9302c;
    --backspace-bg: #f0ad4e;
    --backspace-hover: #ec971f;
    --text-color: #333;
    --operator-text: #fff;
}
body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    font-family: Arial, sans-serif;
    margin: 0;
    background: linear-gradient(#efefef, #ffffff, #e5e5e5);
}
.calculator {
    background-color: var(--bg);
    border-radius: 20px;
    box-shadow: 0 10px 25px rgba(0,0,0,0.2);
    padding: 20px;
    width: 320px;
    text-align: center;
}
.calculator h2 {
    margin: 0 0 10px 0;
    color: var(--text-color);
    font-size: 1.5em;
}
.display {
    width: 100%;
    height: 80px;
    font-size: 2em;
    background-color: var(--screen-bg);
    border-radius: 10px;
    border: 1px solid #ccc;
    margin-bottom: 15px;
    padding: 10px 15px;
    text-align: right;
    box-shadow: inset 0 2px 5px rgba(0,0,0,0.1);
    overflow-x: hidden;
    white-space: nowrap;
    box-sizing: border-box;
    transition: font-size 0.1s ease;
    color: var(--text-color);
}
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}
button {
    height: 60px;
    font-size: 1.5em;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    transition: 0.2s;
}
button.number {
    background-color: var(--number-bg);
    color: var(--text-color);
}
button.number:hover {
    background-color: var(--number-hover);
}
button.operator {
    background-color: var(--operator-bg);
    color: var(--operator-text);
}
button.operator:hover {
    background-color: var(--operator-hover);
}
button.equal {
    background-color: var(--equal-bg);
    color: var(--operator-text);
    grid-column: span 2;
}
button.equal:hover {
    background-color: var(--equal-hover);
}
button#clear {
    background-color: var(--clear-bg);
    color: var(--operator-text);
}
button#clear:hover {
    background-color: var(--clear-hover);
}
button#backspace {
    background-color: var(--backspace-bg);
    color: var(--operator-text);
}
button#backspace:hover {
    background-color: var(--backspace-hover);
}