Grids and lines

Site URL: https://garbett.com.au/

Hey guys,

I started designing a website portfolio and I want to use grids similar to the site link I added, but squarespace doesn't seem to have any option of adding such grids besides the lines in the content blocks. Besides that, If I use the line features I don't know how I can add it so it's from one end to the other to the page.

Do you have any advise on how I could reach a similar result to the one in the website I'm giving as an example ? 

Thanks a bunch!

Adina Coteanu