Read about header_wrap class but was not in files

I read about how to correct the .header_wrap class in css but when I went to increase it there was none in either the layout.css or template_css.
I added to both and no effect.

I see .header { etc.
But there was NO .header_wrap
Can you please tell us which file css it should be in, how it is referenced, and if something else could override it?

I've looked at all template files through joomla and have started looking in file manager through other folders.

Thanks,

In template_css.php

.header_wrap {
height: 70px;
...

change height parameter