Page Speed Insight (FCP + LCP) for Mobile - CSS delivery

I'm looking for someone who will improve FCP and LCP on mobile. So far everything was set up with WP Rocket except off the CSS delivery. WP Rocket breaks the layout slightly with standard setting. JS delivery is already sorted out.

Technology used on website:
Wordpress
Astra Pro Theme
Elementor Pro
WP Rocket
Siteground Hosting with PHP 7.4.2
Cloudflare CDN

Requirements:
- Improve to Pagespeed insight mobile score to at least 80 mark without decreasing desktop score
- Speed up CSS delivery without breaking the layout and increasing CLS.

Pages/type of pages to improve
1. https://www.swissvans.com (Main Page)
2. https://www.swissvans.com/product-category/manufacturers/vw-vans/t6-kombi-vans/ (Product Archive)
3. https://www.swissvans.com/product/ford-transit-custom-sport/ (Regular Product Page)
4. https://www.swissvans.com/product/vw-transporter-kombi-lease/ (Custom Product Page)
5. https://www.swissvans.com/product/ford-transit-custom-lease/ (Custom Product Page)
6. https://www.swissvans.com/blog/2021/transit-custom-super-style/ (Blog Post)

Project will be divided by 6 millstones for each of this page types/pages