Stick the menu color

I have a problem. I want that the color of my menu always have the same color. Normaly it is transparent. I want it as in the pictures.

Sorry for my bad english.

best regards

Hi,

Add this CSS code below to Customize > additional CSS:

.site-header {
    background-color: rgba(255, 255, 255, 0.8);
}

Regards,
Awan

Thank´s that´s it! Do you know how I can get the header a little bit smaller?

best Regards

Already replied in here A smaller menu bar