Use multiple css classnames in react js

Question

i would like to resize my button and i understand i will need to use classname for this.

Here's my component

              <Tour
                steps={steps}
                isOpen={this.state.isTourOpen}
                onRequestClose={this.closeTour}
                rounded={5}
                className="reactour_helper_large"
              />

Here's my CSS code

.reactour_helper_large{ 
    max-width: 80% 
}
.reactour_close{ 
    width: 15px;
}

Here's the HTML code

I am able to resize my tab using reactour_helper_large. However when i put something like className="reactour_helper_large reactour_close", the css for reactour_close gets applied on the main tab as well. How do i edit it such that it only applies for the button class highlighted below? Thank you.