To move an element on the Z-axis without triggering layout or paint operations, you can use the transform property with the translateZ(0) function. This is often used to create a new stacking context for the element, which can improve rendering performance. It doesn't affect the layout or paint and is ideal for off-screen animations or optimizing 3D transforms.

The correct CSS property that specifies the duration of an animation is animation-duration. It allows you to define how long the animation will take to complete, typically in seconds (s) or milliseconds (ms). This property is crucial for controlling the speed and timing of animations.

The currentColor value in CSS represents the computed color value for text inside an element. It allows you to set properties like border or padding to the same color as the text content, ensuring consistent styling.

In SASS/SCSS, the @mixin directive allows for the creation of reusable chunks of CSS. Mixins are blocks of styles that can be included and reused in different parts of your stylesheet. They are a powerful way to keep your styles modular and maintainable.

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.