How to use the webencodings.decode function in webencodings

if protocol_encoding:
        fallback = lookup(protocol_encoding)
        if fallback:
            return decode(css_bytes, fallback)
    if css_bytes.startswith(b'@charset "'):
        # 10 is len(b'@charset "')
        # 100 is arbitrary so that no encoding label is more than 100-10 bytes.
        end_quote = css_bytes.find(b'"', 10, 100)
        if end_quote != -1 and css_bytes.startswith(b'";', end_quote):
            fallback = lookup(css_bytes[10:end_quote].decode('latin1'))
            if fallback:
                if fallback.name in ('utf-16be', 'utf-16le'):
                    return decode(css_bytes, UTF8)
                return decode(css_bytes, fallback)
    if environment_encoding:
        return decode(css_bytes, environment_encoding)
    return decode(css_bytes, UTF8)

(e.g. via the ``charset`` parameter of the ``Content-Type`` header.)
    :param environment_encoding:
        A :class:`webencodings.Encoding` object
        for the `environment encoding
        `_,
        if any.
    :returns:
        A 2-tuple of a decoded Unicode string
        and the :class:`webencodings.Encoding` object that was used.

    """
    # http://dev.w3.org/csswg/css-syntax/#the-input-byte-stream
    if protocol_encoding:
        fallback = lookup(protocol_encoding)
        if fallback:
            return decode(css_bytes, fallback)
    if css_bytes.startswith(b'@charset "'):
        # 10 is len(b'@charset "')
        # 100 is arbitrary so that no encoding label is more than 100-10 bytes.
        end_quote = css_bytes.find(b'"', 10, 100)
        if end_quote != -1 and css_bytes.startswith(b'";', end_quote):
            fallback = lookup(css_bytes[10:end_quote].decode('latin1'))
            if fallback:
                if fallback.name in ('utf-16be', 'utf-16le'):
                    return decode(css_bytes, UTF8)
                return decode(css_bytes, fallback)
    if environment_encoding:
        return decode(css_bytes, environment_encoding)
    return decode(css_bytes, UTF8)