下面这段代码使用正常模式能定位到输入框，为什么使用无头模式就定位不到输入框了呢？
from selenium import webdriver
from bs4 import BeautifulSoup
from selenium.webdriver.common.by import By
from selenium.webdriver.support.ui import WebDriverWait
from selenium.webdriver.support import expected_conditions as EC
url = 'http://ehall.jit.edu.cn/new/index.html'
chrome_options = webdriver.ChromeOptions()
chrome_options.add_argument('--headless')
browser = webdriver.Chrome('D:/Python36-32/Scripts/chromedriver.exe', chrome_options=chrome_options)

browser = webdriver.Chrome('D:/Python36-32/Scripts/chromedriver.exe')

browser.get(url)
wait = WebDriverWait(browser, 15)
input_denglu = wait.until(EC.element_to_be_clickable((By.CLASS_NAME, 'amp-no-login-zh')))
input_denglu.click()
input_username = wait.until(EC.presence_of_element_located((By.ID, 'username')))
input_username.clear()
input_username.send_keys(user)
input_password = wait.until(EC.presence_of_element_located((By.ID, 'password')))
input_password.clear()
input_password.send_keys(pad)