Regex - return match between strings in template literals

Question

I want to match all strings between custom string, so here we go:

var string = `

    <!--@hello-dear:John-->
    <h1>John</h1>
    <!--@bye-dear:John-->

`;

var startString = "<!--@hello-dear:John-->";
var endString   = "<!--@bye-dear:John-->";

var regString = startString + "(.*?)" + endString;
var regex     = new RegExp(regString, "i");

console.log(string.match(regex));

Returns null

Expected that matched object with the string

"<!--@hello-dear:John-->
<h1>John</h1>
<!--@bye-dear:John-->"