Make header a solid color on scroll

Can anyone help me make the header menu a solid color on scroll? I want it to overlay the image when you enter the site, but change to a solid color once you scroll.
The site is
Thanks so much!

You can use this CSS

.fl-theme-builder-header-scrolled  .fl-row-content-wrap {
    background-color: rgba(66,85,99,1)!important;