In SASS/SCSS, a mixin is defined using the @mixin directive followed by the mixin name and parentheses. The correct syntax is @mixin myMixin() { ... }. Mixins are used to encapsulate reusable sets of styles and can take parameters inside the parentheses if needed.

When you apply the CSS float property to an element, it is removed from the normal document flow. This means that other elements may flow around it as if it doesn't occupy space.

In the CSS box model, the "content" area is the space where content, such as text or images, is displayed. This is the innermost part of an element's layout and is surrounded by padding, border, and margin.

To reveal or hide portions of the background based on the foreground content, you can use background-clip: text;. This property allows the background to show through the text or other foreground elements, creating an interesting visual effect.

The CSS property that adjusts the space between lines of text is "line-height." It is used to control the vertical space between lines, making text more readable and aesthetically pleasing. A larger value increases the line spacing, while a smaller value decreases it.

The 'padding' property in CSS affects the space inside an element. It determines the spacing between the element's content and its border, creating internal space.

The grid-area property is used to span multiple rows and columns in a grid layout. By defining the starting and ending grid lines within this property, you can control how many rows and columns your grid item spans.

To overlay a button on the bottom right corner of an image, you should position it absolutely and use "bottom: 0; right: 0;" to place it at the specified location relative to its nearest positioned ancestor or the viewport.

To make an animation pause and resume on hover, you can combine the animation-play-state property with the :hover pseudo-class on the element you want to affect. By setting animation-play-state: paused; on hover, you can pause the animation, and by setting it to running, you can resume it.

When a custom web font isn't supported or doesn't load, the browser will default to a "sans-serif" font. This is a fallback font that is widely available on most systems and ensures that text remains readable even when the custom font is unavailable.