JSFiddle - React, Tailwind, and code Playground

HTML

<div id="container">
    <div id="centerbox">
        <div id="floater"></div>
    </div>
    Resize the window <b>CAREFULLY</b> and notice that sometimes the red box is precisely within the back square, and sometimes it's 1px off.
</div>

CSS

#container
            {
                background-image: url('data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAB9AAAADICAMAAACHxIozAAAABlBMVEUAAAD///+l2Z/dAAACq0lEQVR42u3VQQ0AMAzEsHX8OXcoWuk0G0I+uQUAxLsHAIhn6ABg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChAwCGDgAYOgBg6ABg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChAwCGDgAYOgBg6ABg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChAwCGDgCGDgAYOgBg6PCtXqAyGDowrcZpDIYOABg6AGDoAGDoAIChAwCGDgAYOgAYOgBg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChAwCGDgAYOgBg6ABg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChAwCGDgAYOgBg6ABg6ACAoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChAwCGDgAYOgBg6ACAoQOAoQMAhg4AGDoAYOgAYOgAgKEDAIYOABg6ABg6AGDoAIChAwCGDgCGDgAYOgBg6ACAoQOAoQMAhg4AGDoAYOgAYOgAgKEDAIYOABg6ABg6AGDoAIChAwCGDgCGDgAYOgBg6ACAoQOAoQMAhg4AGDoAYOgAYOgAgKEDAIYOABg6AGDokKfHaQyGDkyrBSqDoQMAhg4AGDoAGDoAYOgAgKEDAIYOAIYOABg6AGDoAIChA4ChSwAAhg4AGDoAYOgAgKEDgKEDAIYOABg6AGDoAGDoAIChAwCGDgAYOgAYOgBg6ACAoQMAhg4Ahg4AGDoAYOgAgKEDgKEDAIYOABg6AGDoAGDoAIChAwCGDgAYOgAYOgBg6ACAoQMAhg4Ahg4AGDoAYOgAgKEDgKEDALEeYdfPYfw5pLEAAAAASUVORK5CYII=');
                background-position: center top;
                background-repeat: no-repeat;
                min-width: 302px;
                background-color: yellow;
                border: 1px solid blue;
            }
            #centerbox
            {
                width: 300px;
                height: 300px;
                border: 1px solid lime;
                margin: auto;
                position: relative
            }
            #floater
            {
                position: absolute;
                top: 50px;
                left: 101px;
                width: 98px;
                height: 98px;
                background-color: red;
            }