How can I prevent my widget styles clashing with existing styles in different websites?

I have a chatbot widget and i am placing it in different websites for different customers. Customers add it to their sites using a single script tag right before the end of </body> tag. However, in different websites already existing stylesheets like Materalize or main css file interfere with my css and prevent some crucial functions to work. How can i overcome this? There is no classname clash by the way. All my classnames have unique codes for my widget. Should i mark all my styles as !important?