Hi,
Thanks for contacting us.
1. You should backup Custom file (Custom CSS or Custom Code)file before updating our theme & plugins when the newest version will be released.
Or 2. You can create a Child Theme to write Custom CSS segment, it won't loose when updating the newest version.
For your issue, you can use another way by adding Custom CSS segment on Customizer > Custom Code > Custom CSS to fix this issue:
@media(max-width:768px){
.blog #main .entry-header h2{
font-size:16px !important;
margin-left: -54px
}
}
You can use appropriate ways for your website.
Best Regards,
YoloTheme