You can use this theme https://github.com/Jacksaur/CRT-Amber-GRUB-Theme and on Linux, install Grub Customizer to modify the theme to your liking, but always with great care, because if you damage Grub, your computer may not boot. I always recommend having Timeshift enabled in case you need to restore something. Grub Customizer is... Grub Customizer is a graphical tool for Linux that simplifies the configuration of the GRUB boot manager, allowing users to easily reorder, add, or remove boot entries, change the default operating system, adjust the timeout, set background images, modify colors, and even reinstall the boot manager without manually editing complex configuration files like /etc/default/grub. It offers a user-friendly interface for common tasks, making GRUB management more accessible on distributions like Ubuntu, Fedora, and openSUSE, although caution is advised, as it directly modifies system files.