Hi Andrea,
You can do this in css.
Here is class that you can apply to your header
.sticky-header {
margin: 0;
padding: 0;
width: 100%;
top: 0;
z-index: 101;
position: -webkit-sticky;
position: sticky;
}
If you need to support IE, you can use this
.sticky-container {
height: 175px;
}
.sticky-header-fixed {
margin: 0;
padding: 0;
width: 100%;
top: 0;
z-index: 101;
position: fixed;
}
Where you put a container around your header and add the class sticky container and define the height manually. So play around with that value. Then apply the class sticky header fixed to your header.
Here is some documentation on changing the style sheets
https://docs.mendix.com/howto50/setup-mendix-ui-framework-with-koala
Hope this helps!