What are some of the "gotchas" for writing efficient CSS?

Here are some common "gotchas" to keep in mind when writing efficient CSS:

1. Avoid using too many CSS selectors: Using too many selectors to target specific elements can make your CSS code more complex and harder to maintain. Additionally, it can also make the browser work harder to match selectors to the elements on the page, which can slow down rendering.
2. Avoid using too many CSS properties: Similarly, using too many CSS properties can make your code more complex and harder to maintain, and it can also slow down the rendering process by making the browser work harder to apply the styles.
3. Use CSS preprocessors sparingly: CSS preprocessors like SASS and LESS can make your code more maintainable and allow you to use variables and functions, but they can also add an extra step to the build process, which can slow down the page load time.
4. Be mindful of the CSS box model: The box model is the way that the browser calculates the size and position of elements on the page. Understanding how the box model works and how to use it effectively can help you write more efficient CSS.
5. Use CSS methodologies: CSS methodologies like BEM, OOCSS, and SMACSS can help you write more modular and maintainable CSS.
6. Use CSS frameworks sparingly: While frameworks like Bootstrap and Foundation can be useful for quickly prototyping a layout, they can also add unnecessary code bloat and slow down the page load time.
7. Use CSS minifiers: Minifying your CSS code can help reduce the file size and speed up the page load time.
8. Use CSS properties that are more performant: Some CSS properties like transform and opacity are more performant than others like position:absolute.
9. Avoid using !important: While the !important keyword can be useful in some cases, it can also make your CSS code harder to maintain and debug.
10. Use browser developer tools: Modern browser developer tools can help you identify and fix performance issues with your CSS code.

By keeping these "gotchas" in mind, you can write more efficient CSS that will load faster and be easier to maintain over time.