JSFiddle - React, Tailwind, and code Playground

HTML

<script src="http://d3js.org/d3.v3.js"></script>

CSS

.rule {
    height: 90%;
    position: absolute;
    border-right: 1px dotted #000;
    text-align: right;
}
span {
    margin-right: 0.5em;
}

JavaScript

d3.select('html').on('mousemove', function() {
    var xpos = d3.event.pageX;
    var rule = d3.select('body').selectAll('div.rule')
        .data([0]);
    rule.enter().append('div')
        .attr('class', 'rule')
      .append('span');
    rule.style('left', xpos + 'px');
    rule.select('span').text(xpos);
});