Can I change from Fluid Engine to Classic Editor?

Hi

 have some CSS code I want to add to my site but cannot get it to work properly. To cut a long story short, it apparently only works on Classic Editor blocks not Fluid Engine. Is there a way of adding a Classic Edition block to my site?

L

44 minutes ago, tuanphan said:

You can click Add Section

 

Click Add Blank: Classic Editor

Thank you so much. You are always so helpful @tuanphan