Developer Setting on a Button

I’m playing with some custom setting on a button and I’m not sure how to use the developer setting in the Button. What is the syntax for custom ID attribute in developer setting?

Here is the css code I’d like to use. What do I enter in the Custom ID attribute of the button? .example #example? Is the syntx on my css correct? I’m placing in quick css on general styling page.
Thank you.
Mike

.example {
color: #009345 !important;
text-transform: uppercase;
background: #ffffff;
padding: 20px;
border: 4px solid #009345 !important;
border-radius: 6px;
display: inline-block;
transition: all 0.3s ease 0s;
}

.example:hover {
color: #413f8a !important;
border-radius: 50px;
border-color: #413f8a !important;
transition: all 0.3s ease 0s;
}