How do you know what CSS name an element is to override it

Question

If I see an element such as this in the code, how do I work out what to put in my less file to override the CSS used on it?

button id="bundle-slide" class="action primary customize" type="button"

I believe the background color for this one would be: @button-primary_background

Answer 1

Suppose you want to change background of bundle product button then write down below style in your less file

.bundle-actions {
    .action.primary.customize {
        background-color: @button-background;
    }
}