Hi @core365,
It’s a predefined class from the HTML structure of your added element, example, let’s say this is the element (simplified)
<div class="the_element">
Some static content not meant for editing
<div class="x-text-content-text-primary">the text you added</div>
</div>
When you add a class to an element, like h-responsive
, it will be added to its main structure like this
<div class="the_element h-responsive">
<..... Some static structure not meant for editing ..... >
<div class="x-text-content-text-primary">the text you added</div>
</div>
So in order to make your actual text to be responsive, you must use the selector .h-responsive .x-text-content-text-primary
.
But it happens to be like standard text like this, then just .h-responsive
is enough.
<div class="the_element h-responsive">
the text you added
</div>
As for finding the predefined selectors, you’ll use your browser tool like Google Chrome’s Developer tool (please check this https://developers.google.com/web/tools/chrome-devtools/css/). There, you’ll see the HTML structure of your page where class names are applied, and selectors are always the equivalent of class name, just with dot. Or pound if it’s ID. Examples,
<div class="hello"></div>
== .hello
<div class="hello world"></div>
== .hello.world
(no space)
<div class="hello"><span class="world"></span></div>
== .hello .world
(with space, means a child element).
<div id="hello"><span class="world"></span></div>
== #hello .world
(id and a class, with space too).
And there is no responsive setting in global block, you should always add it within the page/post builder set. But you can add the class name to your global block’s elements then apply the responsive setting to the main page where global block is added, then it’s the same 
Hope these helps.