def human_readable_size(byte_size):
    """Return human-readable size string, using base-10 prefixes."""
    if byte_size < 10**3:
        return f'{byte_size}B'
    if byte_size < 10**6:
        return f'{byte_size / 10**3:.1f}kB'
    if byte_size < 10**9:
        return f'{byte_size / 10**6:.1f}MB'
    return f'{byte_size / 10**9:.1f}GB'