Change the width of the top and bottom border to thick, and the left and right border to thin of a <div> element:
document.getElementById("myDiv").style.borderWidth = "thick thin";
<!DOCTYPE html> <html> <head> <style> #myDiv {//from ww w.j ava 2 s. c o m border-style: solid; } </style> </head> <body> <div id="myDiv">This is a div element.</div> <br> <button type="button" onclick="myFunction()">Change width of the four borders</button> <script> function myFunction() { document.getElementById("myDiv").style.borderWidth = "thick thin"; } </script> </body> </html>