Avia button fullwidth Font size

Hi.

I usually need to change the font size on a full width button and to do this on a “Page” i us ethic score that works 100%

.page-id-xxxx .avia-button-fullwidth { font-size: 50px !important; }

I need to change the font size but on a blog “post” – i have tried the same with no success so tried

.post-id-xxxx .avia-button-fullwidth { font-size: 50px !important; } but no joy can you please advise,

Thanks