To create a media query for screens wider than 768px, you should use the @media rule, followed by the screen keyword (optional) and and (min-width: 768px). The correct option is @media screen and (min-width: 768px) { /* Styles go here */ }.

PostCSS is a popular tool used in web development to automatically add vendor prefixes to CSS properties. It is highly configurable and can be integrated into your build process. PostCSS, along with plugins like Autoprefixer, streamlines the process of making your CSS code cross-browser compatible by adding the necessary prefixes.

When certain properties like opacity and transform are animated, they are considered more performant because they typically don't trigger relayouts or "reflows" in most browsers. Relayouts are costly in terms of performance and can significantly slow down animations.

The "animation-direction" property in CSS allows you to control the direction of an animation. Setting it to "reverse" will make the animation play in the reverse direction, essentially rewinding the animation.

To target both an ordered list (ol) and its list items (li) in a single CSS selector, you should use "ol li" without any comma or additional characters. This selector will apply styles to all li elements within an ol element.

The value of animation-fill-mode that ensures the animation's styles are applied before the animation begins is backwards. When you set animation-fill-mode to backwards, the element retains the styles of the first keyframe until the animation begins. This can be useful to set initial styles before the animation starts.

To create a sidebar that sticks to the top after scrolling past its initial position but stops sticking when it reaches the footer, you should apply the "position: sticky" property. It maintains the element's natural position until a specified scrolling threshold is reached, and then it behaves as if it were fixed.

The "forwards" value for the "animation-fill-mode" property makes the animation continue in its final state after completion. It ensures that the final keyframe of the animation is retained as the end state even after the animation completes.

The positioning value that makes an element positioned relative to its original position is relative. When you set an element's position to relative, you can use properties like top, right, bottom, and left to move it relative to where it would have been in the normal document flow. This can be useful for fine-tuning element placement.

When using CSS to mask an element, the area defined by the mask image that is transparent will be visible. A mask hides or reveals parts of an element based on the transparency of the mask image. Areas in the mask image that are transparent reveal the underlying content.