:root {
    --bg-color: #f0f2f5;
    --calc-bg: #ffffff;
    --text-color: #333333;
    --btn-bg: #e4e6eb;
    --btn-hover: #d8dadf;
    --operator-bg: #1877f2;
    --operator-text: #ffffff;
    --display-bg: #f5f6f7;
    --shadow: 0 4px 15px rgba(0,0,0,0.1);
}

[data-theme="dark"] {
    --bg-color: #18191a;
    --calc-bg: #242526;
    --text-color: #e4e6eb;
    --btn-bg: #3a3b3c;
    --btn-hover: #4e4f50;
    --operator-bg: #2d88ff;
    --operator-text: #ffffff;
    --display-bg: #3a3b3c;
    --shadow: 0 4px 15px rgba(0,0,0,0.4);
}

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    transition: all 0.3s ease;
}

.container {
    width: 320px;
    padding: 20px;
    background-color: var(--calc-bg);
    border-radius: 20px;
    box-shadow: var(--shadow);
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.display {
    background-color: var(--display-bg);
    height: 60px;
    border-radius: 10px;
    display: flex;
    justify-content: flex-end;
    align-items: center;
    padding: 0 15px;
    font-size: 24px;
    margin-bottom: 20px;
    overflow-x: auto;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

.btn {
    height: 60px;
    border: none;
    border-radius: 10px;
    background-color: var(--btn-bg);
    color: var(--text-color);
    font-size: 18px;
    cursor: pointer;
    transition: background-color 0.2s;
}

.btn:hover {
    background-color: var(--btn-hover);
}

.operator {
    background-color: var(--operator-bg);
    color: var(--operator-text);
}

.operator:hover {
    opacity: 0.9;
}

.clear {
    background-color: #fa3e3e;
    color: white;
}

.equal {
    grid-row: span 2;
    height: 130px;
    background-color: #00a400;
    color: white;
}

.zero {
    grid-column: span 2;
}

/* Switch styling */
.switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: #ccc;
    transition: .4s;
}

.slider:before {
    position: absolute;
    content: "";
    height: 18px;
    width: 18px;
    left: 3px;
    bottom: 3px;
    background-color: white;
    transition: .4s;
}

input:checked + .slider {
    background-color: #2d88ff;
}

input:checked + .slider:before {
    transform: translateX(26px);
}

.slider.round {
    border-radius: 24px;
}

.slider.round:before {
    border-radius: 50%;
}