Scrollbar to stop under sticky menu

Hi,

How can recreate what Google does in its My Business webpage ...
mobile view

desktop view

... where the scrollbar starts under the sticky menu?

This is what I have so far:

::-webkit-scrollbar {
    height: 16px;
    overflow: hidden;
    width: 16px;
}

::-webkit-scrollbar-button {
    height: 0;
    width: 0;
}
::-webkit-scrollbar-corner {
    background: transparent;
}
::-webkit-scrollbar-thumb {
    background-color: rgba(0,0,0,.1);
    background-clip: padding-box;
    border: solid transparent;
    border-width: 1px 1px 1px 0px;
    min-height: 28px;
    padding: 100px 0 0;
    -webkit-box-shadow: inset 1px 1px 0 rgba(0,0,0,.1), inset 0 -1px 0 rgba(0,0,0,.07);
    box-shadow: inset 1px 1px 0 rgba(0,0,0,.1), inset 0 -1px 0 rgba(0,0,0,.07);
}
::-webkit-scrollbar-track {
    background-clip: padding-box;
    border: solid transparent;
    border-width: 0 0 0 4px;
}

Thanks!