How do you isolate slide text from busy backgrounds

[reagle]

In this and subsequent slides I am playing with how to isolate text from busy image or iframe backgrounds (with light and dark examples).

I have two CSS classes blur_on_bg and frame_on_bg that I use to make text on a revealjs slide standout and be seen if there's a busy image background behind the text. The CSS is below. However, neither is perfect. blur_on_bg makes the text look too dark and fuzzy; frame on background can still be ugly if there's a lot of text behind. Do you have a technique that improves legibility, whether it is in front of a gradient, solid color, dark or light color, black or white, text, or busy image? Is there a single solution that can do all of this, or do I need a light and dark background variations?

.reveal .blur_on_bg {
    text-shadow: 2px 1px 6px rgba(190,190,190,1.0),
                 2px 1px 8px black;
}

.reveal section.frame_on_bg :is(ul, ol) > li {
    list-style-position: inside;
    margin-left: 70px;
    text-indent: -50px;
}

/* ------ */

.reveal section.frame_on_bg > :is(h2, p) {
    display: inline; /* otherwise highlight width = 100% */
}

.reveal section.frame_on_bg > * {
    background: rgba(252, 250, 235, 0.80);
}

html.dim_background .slide-background {
    opacity: 0.7 !important;
}