The primary difference between a mixin and a function in SASS/SCSS is that functions are used for reusable styles and can return values, while mixins are used for reusable logic and can generate CSS rules. Mixins can accept arguments, which allows for more dynamic behavior, whereas functions are typically used for calculations and value generation.

The primary goal of the OOCSS (Object-Oriented CSS) methodology is to separate content and layout. OOCSS promotes creating reusable and modular CSS classes that can be applied to various elements in a layout, separating the styling from the content. This improves maintainability and promotes a more organized CSS structure.

The ">" combinator is used to target a direct child element, ensuring that styles are applied only to the immediate child and not to nested descendants.

The property in CSS that allows you to apply a delay before an animation starts is the animation-delay. This property is used to create a pause before the animation begins, which is especially useful for sequencing animations.

To ensure that hyperlinks have no underlines by default but are underlined when hovered over, you should use the CSS rule a { text-decoration: none; } to remove the underlines from all anchor elements and then use a:hover { text-decoration: underline; } to specify that underlines should appear when the link is hovered.

Object-Oriented CSS (OOCSS) emphasizes separating the container and content in your styles and promoting the reuse of styles (i.e., CSS rules). This approach helps keep your CSS modular, making it easier to maintain and reducing redundancy in your code.

In Styled Components, you can dynamically change the style of a component based on its props by using the style prop. You can pass in an inline CSS object and conditionally apply styles based on the values of the props. This allows for the creation of versatile and reusable components.

The default value of the 'box-sizing' property in CSS is 'content-box.' In this mode, the width and height of an element do not include padding or borders, only the content is considered. This can sometimes lead to unexpected layout behavior, which is why 'border-box' is often preferred.

Excessive nesting in SASS or SCSS can lead to bloated and inefficient CSS files, which are larger in size. This negatively impacts loading times and page performance. It is advisable to avoid deep nesting to keep the stylesheet lean and maintainable.

A font's loading performance can be improved by "preloading." Preloading involves using the link element in the HTML to fetch and cache font files in advance, reducing the time it takes to load and render text with custom fonts.