JSFiddle - React, Tailwind, and code Playground

HTML

<div>Line 1</div>
<div>Line 2</div>
<div>Line 3</div>
<div>Line 4</div>
<div>Line 5</div>
<div>Line 6</div>
<div>Line 7</div>

CSS

.debug {
    background-color:#00e000
}

JavaScript

var start

window.onclick = function(event) {
    if (!start) {
        start=true
        event.srcElement.classList.add('debug')
    } else if (event.shiftKey) {
        event.srcElement.classList.add('debug')
        event.cancelBubble = true
        event.preventDefault()
        return false
    }
}