Selenium Compound class names not permitted

I have the below code that clicks on an element to pop up a screen and copy the text in it

el1 = driver.find_element_by_id("keyDev-A")
el1.click()
el2 = driver.find_element_by_class_name("content")
print(el2.text)

However, when I tried to get selenium to click on the button within that popup with

el3 = driver.find_element(By.CLASS_NAME, "action-btn cancel alert-display")
el3.click()

It produces an error message:

invalid selector: Compound class names not permitted

This is the HTML that I am trying to get selenium to click on. The Close button.

<div class="nav">
    <span class="action-btn confirm prompt-display">Confirm</span>
    <span class="action-btn cancel prompt-display">Cancel</span>
    <span class="action-btn cancel alert-display">Close</span>
</div>

How should I be writing el3 in order to click on the Close button?

Leon's comment leads to the correct information that compound class names are no longer supported. What you could do instead is try using css selectors. In your case, the following line of code should help you get the element you want :

el3 = driver.find_element_by_css_selector(".action-btn.cancel.alert-display")

It finds the element with all three classes (action-btn, cancel and alert-display) in the class attribute. Do note that the order of the classes does not matter here and any of the classes may appear anywhere in the class attribute. As long as the element has all three classes, it will be selected. If you want the order of the classes to be fixed, you can use the following xpath :

el3 = driver.find_element_by_xpath("//*[@class='action-btn cancel alert-display']") 

I am late to this question. But I also found a work around by treating the compound classes as a String, using tag_name, and get_attribute('class'), when you are not familiar with Xpath. It needs some more lines of code but it's straight forward and fit for beginners like me.

   elements = driver.find_elements_by_tag_name('Tag Name Here')
        for element in elments:
            className = watchingTable.get_attribute('class')
            print(className)
                if className == 'Your Needed Classname':
                    #Do your things