Just FYI, if you use triple backticks, then you can get better formatting.

`html
<script>
document.body.addEventListener('htmx:xhr:loadstart', function(evt) {
            const body = document.getElementById('main_content')
            body.style.opacity = 0.1
        });
        document.body.addEventListener('htmx:xhr:loadend', function(evt) {
            const body = document.getElementById('main_content')
            body.style.opacity = 1.0
        });
</script>
`