How do you apply CSS for the first and last elements within a nested element?

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You can apply CSS to the first and last elements within a nested element using the pseudo-class selectors :first-child and :last-child.

For example, to apply CSS to the first and last list items within an unordered list, you could use the following code:

ul li:first-child {
  /* CSS for first list item */
}

ul li:last-child {
  /* CSS for last list item */
}

This code will select the first and last children within the unordered list and apply the specified styles to them.