Is it possible to change HTML of header and footer and message details on the forum?

[vinothkannans (Vinoth Kannan)]

@Berto Using css you can easily hide extra custom header when user scrolling down. Sample (in Desktop)

I added custom header in ember plugin outlet above-site-header. Then using below simple css I am hiding it when scrolling

.d-header {
    top: auto;
}

.docked .d-header {
    top: 0;
}