You can put your custom CSS easily via the customizer, for this go to Customizer > Custom CSS/JS and enter your code into the textarea.
Add Custom CSS/JS
You can also put your custom JS directly from the customizer, for this go to Customizer > Custom CSS/JS and enter your code into the Custom JS textarea. For Google Analytics it is not possible anymore to add it in this field as they have changed their method.
Note: You do not need to put the javascript tags.
