I don't understand the big problem with switching different files. Don't we write components and tests in separate files? When we develop a component we add it to other components/views. When you need to add new props to a component, you open up the component file, add your prop, open up your component test file write your tests, if there are any tests fails you go back to component file and fix it there, then if everything works you add your props in the view components. Especially when we are talking about components and component libraries, you don't change the styling every other day especially when design tokens comes from centralised places (spacing, colors, fonts etc.).

What people misses out is CSS should be written in state-based architecture. For example for a button you have idle, hover, active, focus, focus visible, disabled states, and combinations of each button intent (default, primary, destructive, confirmation, warning) and color scheme (dark, light, high-contrast, low-contrast) states. Each of these states should enable-disable or modify some prop of the element, in most cases combination of different elements (sibling, child-parent). Trying to write them in inline classes is a PITA, especially the main concern for choosing that direction is just so we don't have a separate CSS file or need to find a name for the class (if you have a component, which Tailwind creators recommend you should, then you already need to find names for your components).

Also in addition to having separate component, component test and view/layout components; we also have separate hook files, separate state/context/store files. Even the component files doesn't encapsulate its own logic inside the same file anymore as to increase reuse of such logic. Somehow we practice separating almost every thing in the frontend to its own file, but when it comes to CSS it's too much "back-and-forth".