:root {
    --bg-gradient: linear-gradient(135deg, #001524, #15616d);
    --text-color: #ffffff;
    --card-bg: rgba(109, 236, 212, 0.1);
    --button-bg: #ffffff;
    --button-text: #333;
}

body.light {
    --bg-gradient: linear-gradient(135deg, #faf3dd, #ffa69e);
    --text-color: #222;
    --card-bg: rgba(255,255,255,0.6);
    --button-bg: #222;
    --button-text: #fff;
}

body {
    margin: 0;
    font-family: 'Segoe UI', sans-serif;
    background: var(--bg-gradient);
    color: var(--text-color);
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    transition: 0.4s ease;
}

.container {
    background: var(--card-bg);
    padding: 40px;
    border-radius: 20px;
    backdrop-filter: blur(10px);
    text-align: center;
    width: 90%;
    max-width: 400px;
    box-shadow: 0 10px 30px rgba(0,0,0,0.3);
}

h1 {
    margin-bottom: 20px;
}

#display {
    font-size: 3rem;
    margin: 20px 0;
    letter-spacing: 2px;
}

.buttons {
    display: flex;
    flex-wrap: wrap;
    justify-content: center;
    gap: 10px;
}

button {
    padding: 10px 20px;
    border: none;
    border-radius: 30px;
    cursor: pointer;
    font-weight: bold;
    background: var(--button-bg);
    color: var(--button-text);
    transition: all 0.3s ease;
}

button:hover {
    transform: scale(1.1);
    opacity: 0.9;
}

ul {
    list-style: none;
    padding: 0;
    margin-top: 20px;
    max-height: 150px;
    overflow-y: auto;
}

li {
    margin: 5px 0;
    font-size: 14px;
}

.toggle {
    margin-top: 15px;
    font-size: 14px;
    cursor: pointer;
    text-decoration: underline;
}

@media (max-width: 500px) {
    #display {
        font-size: 2.2rem;
    }
}