Selenium : ExpectedConditions is obsolete in C#

Go to Managenuget, search for DotNetSeleniumExtras.WaitHelpers, import that namespace into your class. Now you can do this:

var wait = new WebDriverWait(driver, new TimeSpan(0, 0, 30));
var element = wait.Until(SeleniumExtras.WaitHelpers.ExpectedConditions.ElementIsVisible(By.Id("content-section")));