custom community theme how to css magazine style

Hi

I am wondering if it is easy to css the style of the custom community theme magazine style for posts on the home page.. It comes smaller than I want and with rounded corners…

I have been playing here
https://www.jbcc.oinonendesigns.com/

I want it to look something like this.
https://astrum.purethemes.wpengine.com/ 4 photos on this theme ( square corners.. bigger photo and text)

or is there a plug in that anyone could recommend that would do it

thanks in advance