How to select a selector when a class does not exists - html

Question

I have a doubt about the "sibling selectors" for CSS.
This is the situation:
if in some countries we can show the header but in other countries must not show the header, for example:
<!-- USA page -->
<div class="body">
<div class="header">HEADER</div> <!-- it exists -->
<div class="wrapper">BODY</div>
</div>
<hr>
<!-- Canada page --> <!-- does not have header -->
<div class="body">
<div class="wrapper">BODY</div> <!-- I want to modify this wrapper -->
</div>
I am not sure if it's possible because I can't create a new style for the <div class="wrapper">BODY</div> only for Canada because it's one template for all countries.
it's a twig template
<div class="body">
{% if show-header %} <!-- if true show -->
<div class="header">HEADER</div>
{% endif %}
<div class="wrapper">BODY</div>
</div>
so...I need a purely CSS solution... How I can have a specific style to apply for <div class="wrapper">BODY</div> if the <div class="header">HEADER</div> does not exist in Canada. let's say to change the color of the BODY but not for USA.
I thought that with selector to the :not() pseudo-class like so:
:not(.printable) {
/* Styles */
}
but, what is the approach?

Answer 1

I'm not a pro in twig, but you can play around with conditional classes:
<div class="body">
{% if show-header %} <!-- if true show -->
<div class="header">HEADER</div>
{% endif %}
<div class="{{ country == 'Canada' ? 'wrapper-canada' : 'wrapper-usa' }}">BODY</div>
</div>
Or even use function where you will identify country and return corresponding class name.

Answer 2

If I understand your question, a sibling selector would still work for you. Your sibling selector (the presence of .header) would be an override.
So something like this:
.body .wrapper {
color: red; // Default color
}
.body .header + .wrapper {
color: blue; // Override default color when sibling exists
}
JSFiddle: https://jsfiddle.net/fch3drve/