I stopped styling every screen separately

Today I rebuilt the learning platform's interface on a single design system. The problem had accumulated gradually. Every time I wrote a new screen, I styled it whatever way looked good at that moment. On one screen the button is slightly larger, on another slightly smaller. Here the spacing is 16 pixels, there 20. Looked at separately none of it is wrong, but looked at together the platform does not feel like one thing. So first I wrote down the rules: which colours exist and what each is for, what sizes spacing comes in, what sizes text comes in, how many kinds of buttons there are. I gathered all of that in one place. Then I moved the screens onto those rules. That part is tedious work, but the result showed immediately: the screens became one family. The biggest benefit appeared later. When writing a new screen, the question "how should this button look?" no longer comes up — the answer already exists. Work got faster, and more importantly, a new screen automatically resembles the rest. A design system is not for looking pretty; it is for reducing the number of decisions. Thinking from scratch every time is itself a source of mistakes.