The term "cascade" in CSS (Cascading Style Sheets) refers to the order in which styles are applied to HTML elements. This order determines how styles are prioritized and potentially overridden when multiple style rules apply to the same element. Understanding the cascade is key to effectively managing and customizing styles in your web pages.
### How the Cascade Works: 1. **Source Order**: Styles are applied in the order they are read by the browser. Generally, if two styles conflict, the latter one in the source code will take precedence. So if `style.css` is linked first and `new.css` is linked second, the rules in `new.css` will override the conflicting rules in `style.css`.
2. **Specificity**: Specificity is a measure of how specific a selector is. More specific selectors take precedence over less specific ones, **regardless of source order**. For example, `#idSelector` is more specific than `.classSelector`, which is more specific than `elementSelector`.
3. **Inheritance**: Some CSS properties can be inherited from parent elements. If a property isn’t set on an element but is set on its parent, the child element can inherit that property.
### Overriding Styles in `new.css`: - To override a style rule from `style.css`, define a rule targeting the same element or elements in `new.css` with the desired styles. Due to the source order, these new rules will override the previous ones.
/* In style.css */ p { color: blue; } /* In new.css */ p { /* This will override style.css */ color: red; }
- If you need to override a more specific selector from `style.css`, you’ll need to use an equally or more specific selector in `new.css`.
/* In style.css */ .myClass p { color: blue; } /* In new.css */ .myClass p { /* Overrides because of the same specificity */ color: red; }
### Adding to a Style Rule: - If you want to add to (rather than replace) a style rule from `style.css`, simply define additional properties for the same selector in `new.css`. Properties defined in `style.css` will remain, provided they are not overridden.
/* In style.css */ p { color: blue; } /* In new.css */ p { font-size: 16px; /* Adds a new property */ }
### Important Notes: - **!important**: The `!important` declaration can override any style rule, but its use is generally discouraged because it breaks the natural cascade and can make debugging CSS difficult. - **Testing and Debugging**: Use browser developer tools to inspect elements and see which styles are being applied and from which stylesheet. This tool can also show you the specificity of individual selectors.