How do you use templates in your email designs?

I'm a rookie email marketer in the car dealership industry and I wear too many digital marketing hats to become a pro but some simple, two-column responsive templates coded to send from non-traditional ESP's would be great. I'm prob the minority here but in the car biz we have to send them through CRM tools that like to inject just enough header and footer code to blow out an otherwise beautifully crafted email.

The only template I've found that seems to be coded to protect against this is one I found on EmailOnAcid (https://www.emailonacid.com/blog/article/email-development/code4email) that I keep repurposing because it always comes out looking great on all the main devices. I just plug and play my vehicle specials each month.

My modified version of that template looks like this: https://db.tt/p5BnyuXC

It uses CSS I've never seen anywhere else nor can I find an explanation of how it works like this:

*[class="code4email_center"] {
 text-align: center !important;
 padding:10px !important;
 height:20px !important;
}

Thank you to Litmus and the community for awesome resources!

Apart from boilerplate, I prefer not to use any other kind of templates as they can tunel vision your work. I prefer to create well tailored code for individual campaigns / dedicated templates for customers that will support every tricky part across highest possible number of email clients. Someone may think that I use too much code, but I prefer to not let the browser interpret things on their own - the simpliest example would be to omit align="left/center"right" inside TD, as on most clients it would be left-aligned, and on few others it would be centered.

PS: Of course I use big number of snippets that speed up my work or solve certain problems, but they are the smallest possible templates dedicated to certain tasks.