CSS: ID Selector

The ID selector in CSS is used to select an element based on its id attribute. It is represented by a hash (#) followed by the id value. The ID selector is unique to a single element on a page, making it the most specific selector compared to class and type selectors. Here’s how you use it:

CSS

#elementId {
  /* CSS declarations */
}

For example, if you have an element with id="header", you can style it with the ID selector like this:

CSS

#header {
  background-color: yellow;
  padding: 20px;
}

This rule will apply the specified styles only to the element with id="header".

It’s important to note that each ID value must be unique within an HTML document. Using the same ID on more than one element is invalid HTML and can result in unpredictable behavior. Also, because of its high specificity, overusing ID selectors can make your CSS less flexible and harder to maintain.