Ok, an excuse to try @DavidMtl's new SafeEditor
Had to strip the style 'attribute' from the div-tag in the HTML and leave it 'id'-ed like so:
Like you, did move the CSS to a separate file, say "style.css" and refer to the 'id' of the div:
And an instruction for browsers to load the new 'stylesheet' as well when opening the page:
This went between
</head> in the HTML.
Test: now the blue element does appear ... hopefully in yours too?