quickDarkTheme.js

// video: https://youtu.be/1O5YH1jFVRs
////////////
// CONFIG //
////////////
const backgroundColor = "#000000"
const textColorByTag = {
    "H1":"#7FFFD4",
    "H2":"#7FFFD4",
    "H3":"#7FFFD4",
    "P":"#F5F5DC",
    "SPAN":"#F5F5DC",
    "DEFAULT":"#F0FFFF",
}
// More named colors here: https://www.w3schools.com/colors/colors_names.asp

/////////////////////////////////
// Main Logic after this point //
/////////////////////////////////
const walk = document.createTreeWalker(document.body,NodeFilter.SHOW_TEXT,null,false)
while(textNode=walk.nextNode()){
    const parent = textNode.parentElement
    parent.style.backgroundColor = backgroundColor
    const textColor = textColorByTag[parent.tagName]

    parent.style.color = textColor || textColorByTag["DEFAULT"]
}
console.log("DONE!")