To make an animation run in reverse order, you should use the animation-direction property and set it to alternate. This will cause the animation to play in the reverse direction after each iteration, creating a back-and-forth effect.

In a CSS keyframe animation, the "0%" or "from" keyframe represents the starting point of the animation. It defines the initial state of the animated element. You can set CSS properties and values for this keyframe to specify how the element should look at the beginning of the animation.

When two conflicting styles affect an element, the browser prioritizes the style declared in the last stylesheet loaded. This is known as the "cascading" nature of CSS, where later declarations override earlier ones. Specificity comes into play only if the conflicting styles are in the same stylesheet.

In CSS, class selectors have higher specificity than type selectors. Therefore, if a class selector rule is not being applied, but a rule with three type selectors is, it's likely because the class selector rule has a lower specificity.

'vw' stands for Viewport Width in CSS. It is a relative unit that represents a percentage of the width of the viewport, making it useful for creating responsive designs that adapt to different screen sizes.

To keep the header at the top of the viewport when users scroll, you should use the "position: fixed" property. This makes the element's position relative to the browser window, ensuring it stays in place while the page content scrolls beneath it.

The ::after pseudo-element in CSS is used to insert content after the selected element. It is commonly used for adding decorative elements or additional content after an existing element. By using the ::after pseudo-element and specifying the content property, you can dynamically generate and place content after an element without modifying the HTML structure.

The property that allows you to control the size of tracks (rows and columns) in a grid layout is 'grid-template-columns' for columns and 'grid-template-rows' for rows. These properties let you define the size of the grid tracks using various units like pixels, percentages, or 'fr' units.

The "font-display" property in CSS controls how web fonts are displayed during loading. It's used to manage the flash of unstyled text (FOUT) or invisible text, making it an essential property for optimizing web font performance. Setting it to "swap" tells the browser to use a system font until the custom font is available, reducing FOUT.

To make an animation run indefinitely in CSS, you should use the animation-duration property and set it to infinite. This property specifies the time it takes for one cycle of the animation, and when set to infinite, it ensures that the animation continues to run indefinitely.