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<!DOCTYPE html> <html> <head> <style> #myDIV { border: 3px solid black; width: 300px; height: 300px; } </style> </head> <body> <h1>Change border-width with JavaScript</h1> <p>Click the "Try it" button to change the border-width property of the DIV element:</p> <button onclick="myFunction()">Try it</button> <div id="myDIV"> <h1>Hello</h1> </div> <script> function myFunction() { document.getElementById("myDIV").style.borderWidth = "1px 5px"; } </script> </body> </html>