How to remove the grey line separating the Header and the rest of the site (1.7)

[Oxbow8]

Hello,

Is there a way to remove that sort of grey line (or shadow effect, I don't know) (cf my pic) ?

I am in 1.7 and it's just under the Header. It's very visible if I set all the colors in white.

 

I have the default theme, edited with https://addons.prestashop.com/fr/personnalisation-de-page/17952-configurateur-de-themes-avance-theme-maker.html

 

Thanks so much if someone has an idea !

bar.bmp