css/styles.css

```css
@import url('https://fonts.googleapis.com/css2?family=Poppins:wght@300;400;500;600;700&display=swap');

body {
    font-family: 'Poppins', sans-serif;
    background-color: #121212;
    color: #ffffff;
}

.sidebar {
    background-color: #040404;
}

.upload-area {
    border: 2px dashed rgba(255, 255, 255, 0.2);
    transition: all 0.3s ease;
}

.upload-area:hover {
    border-color: #1DB954;
    background: rgba(29, 185, 84, 0.05);
}

.track-item:hover {
    background: rgba(255, 255, 255, 0.05);
}

.active-nav-item {
    background: rgba(255, 255, 255, 0.1);
}

.active-nav-item::before {
    content: '';
    position: absolute;
    left: 0;
    top: 0;
    height: 100%;
    width: 4px;
    background: #1DB954;
}
```