JSFiddle - React, Tailwind, and code Playground

HTML

<div>
Lorem ipsum dolor sit amet, consectetur adipiscing elit.
Vestibulum condimentum consectetur tellus, at bibendum felis ultrices eu.
Nullam nibh urna, euismod a blandit ut, fermentum a leo. Maecenas pharetra elementum fringilla.
Quisque condimentum, nibh quis elementum porttitor, magna libero malesuada dolor, ut feugiat tortor lectus ac turpis. Integer tristique molestie enim, sit amet commodo risus tempus non.
</div>

CSS

.b {
    font-weight: bold;
}

JavaScript

$(document).keypress(function(e) {
    if (e.which == 13 && e.ctrlKey) {
        var s = getSelection();
        var i = s.baseOffset;
        var j = s.extentOffset;
        var t = $('div').text();
        var t0 = t.substring(0, i) + '<span class="b">' +
                 t.substring(i, j) + '</span>' +
                 t.substring(j);
        $('div').html(t0);
    }
});