I write plain CSS today, which is then scoped to components or bundles of interactivity, and all of those point to major, top-level control sheets that help determine the mode (light/dark/high contrast) and the theme. We tweak small changes up high to effect large platform changes throughout, saving time, energy and headache of the hunt/peck exercise.I do similar things with Tailwind, making global changes by updating a config file instead of a base CSS file. It's not hard and it works well. To be honest, it's not something that really comes up very often. I don't see this as a particular advantage of Tailwind or CSS. I care much more about the day-to-day dev experience.
Prior to using Tailwind I spent about 20 years trying every system you can imagine to manage styles across large websites/apps. I still use the skills I learned when Tailwind doesn't cover an edge case I need. It's fine. Before that I spent about 5 years doing the same with tables and font tags (Adobe Pagemill was awesome). Of all the systems I've used, Tailwind is the easiest to keep neat and tidy. Maybe I'm a terrible dev and other people find CSS really easy to manage, but having spent two decades talking about it with other frontend engineers I'm reasonably certain that's not a common skill. Tailwind makes life much easier for most people.