The adjacent sibling combinator in CSS isn’t a selector on it’s own, but a way of combining two selectors. For example: p + p { margin: 0; } The plus sign (+) is the adjacent sibling combinator, between two paragraph tag (element) selectors. What this means is “select any paragraph tag that is directly after
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The :active pseudo selector changes the appearance of a link while it is being activated (being clicked on or otherwise activated). It’s usually only seen for a split second, and provides visual feedback that the element was indeed clicked. It’s most typically used on anchor links (<a href=”#”>). For instance, here’s CSS that will make anchor links
::after is a pseudo element which allows you to insert content onto a page from CSS (without it needing to be in the HTML). While the end result is not actually in the DOM, it appears on the page as if it is, and would essentially be like this: div::after { content: “hi”; } <div> <!–