For Mac OS users, there is a system setting that may not allow you to tab onto several types of elements in a web page. To change this setting:
Open Settings on your iPhone or iPad.
Scroll down and tap Calendar.
Tap Accounts.
Tap Add Account.
Choose Google.
Enter your Gmail email address and tap Next.
Enter your password, and complete 2-Step Verification if prompted.
On the sync options screen, make sure Calendars is toggled on.
Tap Save.
Open the Calendar app, and your Google events should start syncing shortly.
You can go to Calendar > Accounts > [Your Gmail] anytime to turn calendar sync on/off.