Theme settings : default buttons colors doesn't work

Hello,

I have read this thread that describe the same problem as mine : https://xtemos.com/forums/topic/change-the-background-colors/

I tried to increase PHP max input vars to 10.000 (was previously 1000) but it doesn’t seems to work.
CSS looks like this :

.btn.btn-color-default {
    background-color: #F3F3F3;
    color: #3E3E3E;
}

While the theme settings looks like this : https://cln.sh/GyfnJU

Please can you help ?
Many thanks in advance !