Is there a way to merge CSS class properties from different files in the final one?

Question

css

Conditionally, there are 2 files:
a.css
h1{font-family: tahoma;}
b.css You
h1{font-size: 50px;}
need to get the following result:
h1{font-family: tahoma;font-size: 50px;}
Is it possible to implement using Gulp?

Answer 1

gulp + sass + autoprefixer = one love

Answer 2

https://www.npmjs.com/package/combine-css