def header() -> str:
    """
    Writes the LaTeX header using the settings file.

    The header includes all packages and defines all tikz styles.

    :return: Header of the LaTeX document.
    """
    packages = (
        r"\documentclass[convert={density=300,outext=.png}]{standalone}",
        r"\usepackage[margin=1in]{geometry}",
        r"\usepackage{tikz}",
        r"\usetikzlibrary{quantikz}",
    )

    init = (r"\begin{document}", r"\begin{tikzcd}")

    return "\n".join(("\n".join(packages), "\n".join(init)))