This requires knowledge of CSS Cascading Style Sheets. For the TechNews theme, I will give an example. I just tested this out and it works just fine.
First, read about theme overrides here. https://getpublii.com/dev/theme-overrides/#theme-overrides You will want to follow this procedure.
The CSS file you want to change is main.css.
Look for:
.topbar {
background: var(--color);
padding: 0 1.2142857143rem;
position: absolute;
top: 0;
width: 100%;
z-index: 999;
}
and change position to fixed like so.
.topbar {
background: var(--color);
padding: 0 1.2142857143rem;
position: fixed;
top: 0;
width: 100%;
z-index: 999;
}
Cheers!!