Live support chat box for my website

I need a chat box for my website that acts as a live support for my website. I have created my website on yola, so the code will need to be able to be embedded into my website, With the option to change the script and add keywords, as well as time in between responses, and only replys back when the enter or send button is pressed. I will need the option to change the color, style, and size of the chat box messages that we are sending out. Please only reply if you are experienced in such a project. I have few example that I would like to share before the project is started.