What are CSS text selectors?

As per the following discussions:

CSS text selector :contains doesn't work with Selenium
css pseudo-class :contains() no longer allows anchors
The :contains pseudo-class isn't in the CSS Spec and is not supported by either Firefox or Chrome (even outside WebDriver).
Python based solution
To locate the element with text as Log Out you can use either of the following Locator Strategies:
Using link_text:
element = driver.find_element(By.LINK_TEXT, "Log Out")
Using xpath:
element = driver.find_element(By.XPATH, "//a[text()='Log Out']")
Ideally, to locate the element you need to induce WebDriverWait for the visibility_of_element_located() and you can use either of the following Locator Strategies:
Using LINK_TEXT:
element = WebDriverWait(driver, 20).until(EC.visibility_of_element_located((By.LINK_TEXT, "Log Out")))
Using XPATH:
element = WebDriverWait(driver, 20).until(EC.visibility_of_element_located((By.XPATH, "//a[text()='Log Out']")))
Note : You have to add the following imports :
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.common.by import By
from selenium.webdriver.support import expected_conditions as EC
Java based solution
To identify the element with text as Log Out you can use either of the following Locator Strategies:
linkText:
WebElement element = driver.findElement(By.linkText("Log Out"));
xpath:
WebElement element = driver.findElement(By.xpath("//a[text()='Log Out']"));
Ideally, to identify the element you need to induce WebDriverWait for the visibilityOfElementLocated() and you can use either of the following Locator Strategies:
linkText:
WebElement element = new WebDriverWait(driver, 20).until(ExpectedConditions.visibilityOfElementLocated(By.linkText("Log Out")));
xpath:
WebElement element = new WebDriverWait(driver, 20).until(ExpectedConditions.visibilityOfElementLocated(By.xpath("//a[text()='Log Out']")));
References
You can find a couple of relevant detailed discussions in:
selenium.common.exceptions.InvalidSelectorException with “span:contains('string')”