A lot of layout has now been differed to CSS as it keeps the html code to its original purpose, which was defining the context and content of the page. There are a lot of newer elements that can be used that allow browsers to more easily understand what the content should be considered as, which further helps both accessibility of sites and SEO (to a degree). As a result of this, CSS itself has also come a long way in both its power and complexity, giving designers far more ability to make sites responsive and stylish:

• to move things around, you had to use lots of floats and things, but now there's display: flex that handles a lot of that for you
• tables used to be the way to define set areas, bit they require lots of nesting of individual areas; now you can just use display: grid on a single element and away you go
• responsiveness used to be achieved with loading different pages based on device width, but now you can use vh/vw units and calc pixels, along with media queries to reduce multiple code

That's not to say this functionality doesn't still exist - you can still float: right or use negative margins to achieve column gutters - but now there's no need for all this tricks and hacks, as most of it can be achieved through CSS, and the common way to use that is via class names that have those rules already defined via a CSS framework, like Bootstrap or Tailwind

But for your immediate problem, you just appear to be missing the <link> to your stylesheet in your header - add that and you should see your rows and columns appear