import re


def first_char_index(lines, regex):
    """Get the index of the first position for a description character

    Use this to find where the first character after the : should be placed so
    that each comment can line up.

    :param lines: list of strings to find the index for
    :param regex: Regex to identify the line to compare with

    :returns: The index of the first position for description characters,
              or None if no lines matched the given regex
    """
    for line in lines:
        if re.match(regex, line):
            parts = line.split(":")
            before = len(parts[1])
            after = len(parts[1].strip())
            return len(parts[0]) + 1 + (before - after)

    return None