How to click on this HTML element in Python(Selenium)

Recently, I used selenium to crawl some information on the website. And What I want to do is just clicking 'previous month button'.

So I push 'F12' button on Chrome And find HTML Code like this

So I write code like this

webDriver.find_element_by_css_selector('span.ui-icon ui-icon-circle-triangle-w').click()

But it doesn't work, I changed multiple times changing the code like this

webDriver.find_element_by_css_selector('a.ui-icon ui-icon-circle-triangle-w').click()
webDriver.find_element_by_css_selector('ui-icon ui-icon-circle-triangle-w').click()
webDriver.find_element_by_class_name('ui-icon ui-icon-circle-triangle-w').click()

Any of those don't work. When I tried to use first one of three trial(that is : webDriver.find_element_by_css_selector('a.ui-icon ui-icon-circle-triangle-w').click()), the error pops up like this

selenium.common.exceptions.NoSuchElementException: Message: no such element: Unable to locate element: {"method":"css selector","selector":"a.ui-icon ui-icon-circle-triangle-w"}
 (Session info: chrome=86.0.4240.198)

I don't know why it doesn't work..

Please help