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<html><head><script src="https://ajax.googleapis.com/ajax/libs/jquery/3.7.1/jquery.min.js"></script><script>$(document).ready(function(){ $("#add").click(function(){ $("p").toggleClass("main",true); }); $("#remove").click(function(){ $("p").toggleClass("main",false); });});</script><style>.main { font-size: 120%; color: red;}</style></head><body><p>This is a paragraph.</p><p class="main">This is another paragraph.</p><button id="add">Add class "main"</button><button id="remove">Remove class "main"</button></body></html>