CSS Minify

Hi,
My name is Louis Cook. I need your help.
I have a blog https://www.timesdigit.com where I want to combine all CSS file in single file.
I have seen many blogs do that. But I am unable to combine. I have tried using this plugin https://wordpress.org/plugins/autoptimize/
But when I did, my design was mess up..then I deactivate this plugin.
I aksed one of my friend, he said that he did using theme option. he is using Genesis theme. But I am unable to do, I am using Mythemeshop theme.
If you have any proper guidelines, or blog post link then please share.

Thanks

It's most likely that you have identically named definitions in several files which work when the files are loaded in the correct order. However combining the files may very well change the order of the definitions in the single file so that they don't cascade correctly thus messing up the site. You are probably best leaving the CSS as it is.