Regarding the Cookie Warning I would create a simple mvc portlet and include this in the freemarker template of your theme. 

If you have not created a theme so far I guess the best way to do it is - like you already said - to copy a liferay theme and make the adjustments you need. 

Thanks for answering, Fredi.

But it looks like I need some more advice...

I'm using Liferay IDE 3.9 with Eclipse on Windows and created a new Liferay Module project like described in this old blog post.

The resulting module structure looks like this:

The structure of the classic theme in the portal sources looks like this:

Looks quite different...
I tried two ways to copy the images, css, templates and WEB-INF folder to my new theme.

1. Remove everything under webapp and copy the 4 folders there
2. Remove the main folder and copy the 4 folders to the src folder

However, both ways do not work. Because building (Gradle Task) and deploying (copy WAR to deploy) works, but results in a look thats clearly missing some css styling.

There must be some trick I don't know of...

Thanks! The link you posted and the method described there is working! Regarding the copy of the classic theme: The best way to achive that is to unpack the deployed theme war (from the osgi folder) make your changes and build it with gulb again.

However, if you have only small changes, it might even be simpler to unpack - change - repack the original theme. Because I think one has to do the same work on every release of liferay again anyway.

BUT: making Liferay compliant with the European Law, regarding the cookie rules..., thats kind of a challenge that might be worth a blog post!

The reason is that in Europe we are basically not allowed to place a cookie in the browser without the consent of the user! Plus: the user must have the possibility to reject cookies permanently!

The only exception to this rule are cookies that are 'necessary' to offer the service at all.

But Liferay places cookies for the Session (JSESSION), the guest language (GUEST_LANGUAGE_ID) and the ability to store cookies (COOKIE_SUPPORT) on every visit on the page. To argue that the latter two are 'necessary' is at least.... critical.

Disabling this via portlet.properties is not really an option as this is a per user decision!

The support of Google Analytics, the standard way Liferay supports  it (which is outdated anyway), is also not allowed because of the same reason. For me some specific Javascript and a lot of user information was needed to be compliant with the law.

However! If someone is curious how I solved this: https://www.indie-smarthome.com