Customizing/overiding css markup


#1

I’m new and trying to get a grasp on overriding specific style markup.

As i see it, to change a element on a single page you can add a custom style sheet or just add the markup to head of the document.

.ui.header{
border: 1px solid red;
}

All good

Or, update the entire theme by adding
.ui.header{
border: 1px solid red;
}
to header.overrides in themes, and all is still good

But if the above is added to the header.overrides in the site overrides is has no affect.
Shouldn’t it be global in that it should affect all themes?
What am I missing?

Glen