CSS decides between competing declarations through the cascade. Equal-specificity rules use source order, while a more specific selector can take priority even when a broad rule looks nearby. Inheritance is another path: text can receive a color from its parent when no declaration sets that color on the child. You'll use these rules to style a component without changing its neighbors. That boundary matters. Turning every button green isn't a fix for one alert button that needs green. Compare the target and an unaffected sibling after each edit, then check which declaration supplies the computed value.