Jasper template - Keep Title & Navigation at Top when scrolling

I'm using the Jasper template and I want to keep the menu bar at the top of the screen as I scroll down like this website https://www.etudes-studio.com/.

I've tried a lot of CSS codes I've found online but didn't work. Any help would be amazing! 

It seems you solved with this code?

.header {
    position: fixed;
    left: 0;
    width: 100vw;
    z-index: 1000;
    display: flex;
    flex-wrap: nowrap;
    justify-content: space-between;
}

I think you should edit to this

header.header {
    position: fixed;
    left: 0;
    width: 100vw;
    z-index: 1000;
    display: flex;
    flex-wrap: nowrap;
    justify-content: space-between;
}

Thank you @tuanphan but I tried to copy your code and it doesn't work.

7 hours ago, LL-Studio said:

Thank you @tuanphan but I tried to copy your code and it doesn't work.

Both codes are the similar. However, in some templates, blog titles use the .header class. If you set position: fixed for .header, maybe it will fixed the blog title as well.

@tuanphan I solved it, the problem was that in the Jasper template the header doesn't have background color, so I used this code to add it:

header#header {
    background: #ff0000;
    margin: 0 auto;
    padding: 3vw 5vw;
}

and after I used this code to keep the header when scrolling:

header#header {
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    z-index: 999;
}
div#content {
    margin-top: 8vw;
}