Change header background on scroll

gistfile1.txt

function runOnScroll() {
    const header = document.getElementById("header");
    const bodyScroll = document.getElementsByTagName("body")[0].scrollTop;
    // Chrome
    const htmlScroll = document.getElementsByTagName("html")[0].scrollTop;
     
    if ( bodyScroll >= 400 || htmlScroll >= 400) {
        header.style.background = "#615e5d";
    }
    else{
        header.style.background = "none";
    }
    
 }; 
window.addEventListener("scroll", runOnScroll);