Header does not become transparent

Hi there

I have added the following codes to my custom.css:

#sp-header.header-sticky {
    background: rgba(0, 0, 0, 0) !important;
}

#sp-header {
    background: rgba(0, 0, 0, 0) !important;
}

Header-sticky works. Always and on every page the header becomes transparent when scrolling. But the background for the header is only transparent on the start page. On all other pages it is still white:

https://prnt.sc/KjJ4LV1G1dd_

How can I solve this?

Thank you.
Domi