You can do this with ClassName
with one of the classes
driver.FindElement(By.ClassName("btn-default")).Click(); // or driver.FindElement(By.ClassName("btn")).Click();
Or via CssSelector
with both classes
driver.FindElement(By.CssSelector(".btn.btn-default")).Click();
Edit
Error
The item is not available for click at a point.
means that Selenium cannot see the button, so it cannot click on it. First you need to scroll it
IWebElement button = driver.FindElement(By.ClassName("btn-default")); // locate the button, can be done with any other selector Actions action = new Actions(driver); action.MoveToElement(button).Perform(); // move to the button button.Click();
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