There shouldn’t be any limit You might want to check in incognito to make sure you’re not looking at any stale data.
Re: your development question, you need 2 main things - node.js, and yarn. Node.js is a programming/scripting language that is heavily used by Ghost, and yarn is a tool for node.js to install third-party dependencies. The reason you need these is because the css is written in multiple parts (as you might have seen), and there’s a build step to squoosh them together and optimize it. I prefer using a package manager to install software - for Windows, there’s scoop or chocolatey, for Mac, there’s homebrew, and Linux has one preinstalled