If applied CSS is not working, then try to avoid blank spaces in the CSS. Good CSS: #popup{display:none;position:absolute;height:100px;width:100px;background:#E6E6FA; border: 2px solid black;overflow:auto;} Bad CSS: #popup{ display:none; position:absolute; height:100px; width:100px; ....
Sample Code: <!DOCTYPE html> <html> <head> <style> .button { color:white; font-size:12px; font-weight:bold; border:outset; text-align:center; border-color:black; background-color: black; } </style> </head> <body> <button class="button">Sample Button</button> </body> </html>
<!DOCTYPE html> <html> <head> <style> .overFlowCls { overflow:scroll; width: 200px; height: 65px; } </style> ....