What is the offset of CSS selectors?

The term "offset" in the context of CSS selectors typically refers to the position of an element relative to its parent or to the viewport. However, it's important to clarify that CSS selectors themselves do not have an "offset." Instead, the offset is a property of the elements that are selected, and it is typically accessed and manipulated using JavaScript. The CSS is used to define how the elements look and how they are related to other elements in general terms, it doesn't deal with exact position.

When we talk about offsets, we often refer to properties like `offsetTop`, `offsetLeft`, `offsetWidth`, and `offsetHeight`. These properties provide information about an element's position and dimensions within the document. For example, `offsetTop` gives you the distance between the top of the element and the top of its offsetParent, whereas `offsetLeft` gives you the left-side offset. The offsetParent is the nearest positioned ancestor of the element or the body element if there is no positioned ancestor. In summary CSS is for styling, not for precise positioning.

So, while CSS selectors determine *which* elements are targeted for styling or other manipulations, JavaScript is what provides the mechanism to retrieve and potentially change the actual offset values of those elements. This often is needed in situations like animation or when creating dynamic interactive elements that need to adjust their position on the screen in real-time. Remember that CSS will make elements relative to other elements, such as a block, while JavaScript can make changes to the element's position relative to the entire document, or another specific element.