how to merge CSS files?

Hello,
I have checked my website https://locksmiths.ae/ in different website checkers and all suggest to me there are more CSS files on my website can anyone suggest how I can merge them or make it less. I have little knowledge about the coding
Thanks,

 

Merge your CSS files

1. On the Admin sidebar, go to Stores > Settings > Configuration.
2. In the left panel, expand Advanced and choose Developer.
3. Expand the CSS Settings section. CSS Settings.
4. Set Merge CSS Files to Yes .
5. When complete, click Save Config.

 

you can use any online to merge all css files in one,
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