HTML

How to make a full-page div image

https://www.w3schools.com/howto/howto_css_full_page.asp

CSS flexbox (easy way to align content)

https://css-tricks.com/snippets/css/a-guide-to-flexbox/

div as wide as its content

display: inline-block;

or

width: fit-content;

Center a div

    display: block;
    margin: 0 auto;
    width: fit-content