How to make sticky header or fixed header with out plugin

go to dashboard > Customize > CSS > Past this Code

.ast-mobile-header-wrap {
position: fixed;
top: 0;
left: 0;
width: 100%;
z-index: 9999;
background-color: #FCEDEC;
}

this Code for mobile meny header

you have to find out your header Label by Inspect and replace it