Secondary backdrop without Flash

[feifyKike]

Objective

Create an option to enabled to a secondary background color that would be visible only on over-scroll and vertical scroll bounce. Also would color the top and bottom margins in mobile.

Technical issue

onMounted(() => {
  document.body.style.backgroundColor = "#hex"
})

May seem like the simplest solution, however, on anchor tag navigations and initial loads would flash with the "#hex" color.
Need a way to circumvent this.