def apply_styles(graph, styles):
    """
    Apply the styles to a Graphviz graph.
    """
    graph.graph_attr.update(
        ('graph' in styles and styles['graph']) or {}
    )
    graph.node_attr.update(
        ('nodes' in styles and styles['nodes']) or {}
    )
    graph.edge_attr.update(
        ('edges' in styles and styles['edges']) or {}
    )
    return graph