XF 2.0 XF-Re-Designed: How to setup 3 columns pages with different dimensions?

[3rd AnGle]

How can i achieve this kind of 3 column pages?

1. create a left sidebar where the width could be Y px
2. create a right sidebar where the width could be X px

Any help is highly appreciated.

(My end goal is to create an awesome portal kind of page which looks like SPA. I am using @RobParker 's Portal guide https://xenforo.com/community/resources/page-as-portal-homepage.5663/ to achieve this).