Change header panel background color

[girtri]

I'm looking for how to change the header panel background color on Magento 2.
I have a theme that inherit from the standard blank theme.

"Theme path" is <magento folder>/app/design/frontend/<Vendor>/<theme>
In my theme at "web/css/source" I've created "_theme.less" file adding this line:
@header-panel__background-color: @color-blue1;
but nothing happens (clearing cache, pub/static/ecc... files, the "var" folder too but nothing change)

then I tried to add, in my them path, this:
"Magento_Theme/web/css/source/_module.less"
with the same content
@header-panel__background-color: @color-blue1;
but nothing happens..

I see in Luma theme the top header panel is gray: how to get it works?
Thanks in advance

[girtri · Accepted solution]

due to the fact that I inherit from blank theme, the solution is to add this lines in "web/css/source/_theme.less"

.page-header {
    .panel.wrapper {
        .lib-css(background-color, @color-orange-red1);
    }
}