Creating a Web-based button in client

Hello Everyone. An user came up to me with an issue of creating a web-based button in client. I was able to show her where she can put the correct onClick formula but the look of the button is not the same on the Web as it is in Client. I tried entering some HTML code in the button’s properties and was able to change the size of the button but could not get the background color and the shape of the button to show up properly. Does anyone have any suggestions? Thanks for your help in advance!