id in a grid row

On this page, I have a grid row with one cell and a text block and inside a h2 (COMERSO présente la seule solution clef en main et sécurisée
qui valorise vos invendus en conformité avec la législation en vigueur.)
I want to give a different style to this h2 compared to the other h2 of the site.
For the moment I’ve put <h2 style=”text-align: center; text-transform: none; font-size: 32px;”> directly in the text block
But it’s not relevant I’d like to put this style in css (to be able to reduce the font size on mobile). I’ve seen that in the grid row, we can add a ID section. I’ve put “ent-asso” and I also tried “#ent-asso”, which one should I enter in the grid row id section.
And then, how can I change the h2 style properly? I’ve tried several things but I don’tmanage to do it.
#ent-asso h2 { }
#ent-asso #top #wrap_all .main_color h2 { }

Hope it’s clearer, tx !!

Perfect tx !