Struggle with several elements


I have several problems on my site that I can’t solve:

Enlarge the navbar so that I can insert some text and it cuts into the image part.

The black button at the top: I can’t change its color when I hoover on it.

The slider images: I can’t change the 3rd image. Also, I can’t add an opaque background to allow a better readability of the image.

The text on the left below the logo: it is always underline, I do not understand why and I would like to remove it.

best regards