To ensure that the animation effects persist after the animation completes, you should set the "animation-fill-mode" property to "forwards." This will make the animation retain its final state after completing its execution.

The CSS property used to create animations by gradually changing from one set of CSS styles to another is keyframes. Keyframes are used to define a sequence of style changes over a specified duration using the @keyframes rule. The animation duration can be controlled by the animation-duration property.

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 mask-composite property in CSS is used to determine how a mask image should be combined with the element it's applied to. It's used to control the blending mode of the mask image with the element, allowing for various effects.

To make a row of items wrap onto the next line when there isn't enough space in a Flexbox layout, you would adjust the flex-direction property to "column" (for vertical stacking) and flex-wrap to "wrap." This allows the items to stack vertically when space is limited.

To pause an animation before it begins or between iterations, you should use the animation-play-state property. By setting it to paused, you can temporarily halt the animation. This is useful for creating interactive animations and controlling when they start or stop.