:root {
    --bg-color: #ffffff;
    --text-color: #111111;
    --accent-color: #007aff;
}

[data-theme="dark"] {
    --bg-color: #121212;
    --text-color: #f0f0f0;
    --accent-color: #0a84ff;
}

body {
    margin: 0;
    font-family: 'Helvetica Neue', sans-serif;
    background-color: var(--bg-color);
    color: var(--text-color);
    transition: background-color 0.3s ease, color 0.3s ease;
}

header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    padding: 1rem 2rem;
    background: var(--bg-color);
    position: sticky;
    top: 0;
    z-index: 1000;
}

nav a {
    margin-right: 1rem;
    color: var(--text-color);
    text-decoration: none;
}

#hero {
    text-align: center;
    padding: 4rem 2rem;
    background: linear-gradient(120deg, var(--accent-color), #90caf9);
    color: white;
}

section {
    padding: 2rem;
}

.placeholder {
    width: 100%;
    height: 200px;
    background: #ccc;
    border-radius: 16px;
    margin: 1rem 0;
}

.placeholder.small {
    height: 100px;
    width: 150px;
}

.placeholder.medium {
    height: 150px;
}

footer {
    text-align: center;
    padding: 2rem;
    background: var(--bg-color);
}

@media (max-width: 768px) {
    nav a {
        display: block;
        margin: 0.5rem 0;
    }
    header {
        flex-direction: column;
    }
}