To set a fallback font in case the primary font fails to load, you can use the font-family property and specify multiple font names in a comma-separated list. The browser will use the first font in the list that it can find and load. This ensures that even if the primary font is unavailable, the text will still be displayed using an alternative font.

Autoprefixing tools, like Autoprefixer, analyze CSS and add or remove vendor prefixes to ensure compatibility across different browsers. They use data from browser user agents (e.g., Chrome, Firefox) to determine which prefixes are required for specific CSS properties.

When you want to generate multiple class or ID variations in SASS, you would typically use placeholder selectors, also known as %placeholders. These selectors allow you to define styles that can be included in other selectors using the @extend directive, promoting reusability and ensuring cleaner CSS output.

When 'box-sizing' is set to 'content-box,' the total width of an element includes padding and border. The content width does not include these, but the total width does.

The technique where a low-quality or system font is displayed initially and then replaced with a higher-quality custom font when it's loaded is known as "Font FOUT" or "Flash of Unstyled Text." This approach improves perceived performance and ensures a smoother transition between fonts.

The animation-fill-mode: forwards; property-value combination holds the final keyframe styles after the animation finishes. This means that after the animation completes, the element retains the styles from the final keyframe. This can be useful for maintaining a particular state after the animation finishes.

When an element has a 'position: sticky;' property and scrolls past its container, it sticks to the container until it reaches a specified offset, after which it scrolls along with the container. This behavior is often used for navigation bars.

The property commonly used to control the speed curve of a transition effect in CSS is transition-timing-function. This property allows you to specify how the intermediate property values are calculated over the duration of the transition, giving you control over the timing and pace of the transition.

To create a smooth heartbeat animation that makes an icon grow and shrink, you should use the scale transformation with CSS animations. This allows you to scale an element up and down smoothly, ensuring it runs seamlessly in both directions.

The CSS pseudo-class :not() is used to select elements that do not match a specific criteria. It is used to exclude elements that would typically be selected by a CSS selector. For example, :not(.classname) selects all elements that do not have the specified class.