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<!DOCTYPE html> <html> <head> <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script> <script> $(document).ready(function(){ $("#btn1").click(function(){ $("p:first").css("background-color", "red"); }); $("#btn2").click(function(){ $("p:first-child").css("background-color", "yellow"); }); }); </script> </head> <body> <button id="btn1">:first</button> <button id="btn2">:first-child</button><br><br> <div style="border:1px solid"> <p>The first paragraph in div.</p> <p>The last paragraph in the div.</p> </div><br> <div style="border:1px solid"> <p>The first paragraph in another div.</p> <p>The last paragraph in another div.</p> </div> </body> </html>