Make words bold

[wtichentw]

HI, I installed tmuxline recently, I really like it
but i want to customize a little with the font weight
I've traced the vim_statusline_1.vim and would like to change some window name's font weight
but it seems the font weight is accompanied with color
and I can't change font weight only due to the original parameter statusline_nc

so, my question is
what should I do to only make the number "17" as bold as the upper "NORMAL" word

thanks