Solution: Combinator explains the relationship between the selectors. There are four combinators in CSS, child selector (>), adjacent sibling selector(+), general sibling selector(~), descendent selector (space).

Solution: General sibling selector selects all elements that are siblings of a specified element, adjacent sibling selector selects all elements that are adjacent siblings of the specified element, child selector selects all elements that are immediate children of the specified element.

Solution: counter() or counters() function adds value of counter to an element, content inserts generated content, counter-increment increments a counter value, counter-reset creates or resets a counter.

Solution: border-image-slice specifies how to slice border image, border-image-outset specifies the amount by which border image area extends beyond the border box, border-image is a shorthand property for setting all the border-image properties.

Solution: TrueType (TTF) is a font standard developed in the late 1980s by Microsoft and Apple. It is the most common font format for both Microsoft Windows and Mac OS operating systems.

Solution: OpenType (OTF) is a format scalable for computer fonts, it was built on TrueType, and is a registered trademark of Microsoft. These fonts are used commonly today on major computer platforms.

Solution: WOFF is font format used in web pages. It was developed in 2009. It is essentially OpenType or TrueType with compression and additional metadata. The goal is to support font distribution from the server to client over the network with bandwidth constraints.

Solution: When the value is set to alternate the animation is played forwards first then backward. When a value is set to alternate-reverse, the animation is played backward first, then forwards. At normal value the animation is played as normal, this is the default value.

Solution: ease-in specifies an animation with a slow start, ease-out specifies an animation with a slow end, linear specifies animation with same speed from start to end, ease specifies an animation with a slow start, then fast, then end slowly.

Solution: animation-fill-mode property specifies the style for the target element when an animation is not playing. There are four values for this property namely none, forwards, backwards, and both. None is the default value.