The internet has been around for a long while, and over time we’ve changed the way we think about web design. Many old techniques and ways of doing things have gotten phased out as newer and better alternatives have been created, and we say that they have been deprecated.
Deprecated. It’s a word we use and see often. But have you stopped to think about what it means in practice? What are some examples of deprecated web elements, and why don’t we use them any more?
What is deprecation?
In everyday English, to “deprecate” something is to express disapproval of it. For example, you might be inclined to deprecate a news story you don’t like.
When we’re speaking in a technical sense, however, deprecation is the discouragement of use for an old feature. Often, the old feature remains functional in the interests of backward compatibility (so legacy projects don’t break). In essence, this means that you can technically still do things the legacy way. It’ll probably still work, but maybe it’s better to use the new way. 
Another common scenario is when technical elements get deprecated as a prelude to their future removal (which we sometimes call “sunsetting” a feature). This provides everybody time to transition from the old way of working to the new system before the transition happens. If you follow WordPress at all, they recently did this with their radically new Gutenberg editor. They shipped it, but kept an option available to revert to the “classic” editor so users could take time to transition. Someday, the “classic” editor will likely be removed, leaving Gutenberg as the only option for editing posts. In other words, WordPress is sunsetting the “classic” editor.
That’s merely one example. We can also look at HTML features that were once essential staples but became deprecated at some point in time.
Why do HTML elements get deprecated?
Over the years, our way of thinking about HTML has evolved. Originally, it was an all-purpose markup language for displaying and styling content online.
Over time, as external stylesheets became more of a thing, it began to make more sense to think about web development differently — as a separation of concerns where HTML defines the content of a page, and CSS handles the presentation of it.
This separation of style and content brings numerous benefits:
Avoiding duplication: Repeating code for every instance of red-colored text on a page is unwieldy and inefficient when you can have a single CSS class to handle all of it at once. Ease of management: With all of the presentation controlled from a central stylesheet, you can make site-wide changes with little effort.Readability: When viewing a website’s source, it’s a lot easier to understand the code that has been neatly abstracted into separate files for content and style. Caching: The vast majority of websites have consistent styling across all pages, so why make the browser download those style definitions again and again? Putting the presentation code in a dedicated stylesheet allows for caching and reuse to save bandwidth. Developer specialization: Big website projects may have multiple designers and developers working on them, each with their individual areas of expertise. Allowing a CSS specialist to work on their part of the project in their own separate files can be a lot easier for everybody involved. User options: Separating styling from content can allow the developer to easily offer display options to the end user (the increasingly popular ‘night mode’ is a good example of this) or different display modes for accessibility. Responsiveness and device independence: separating the code for content and visual presentation makes it much easier to build websites that display in very different ways on different screen resolutions.
However, in the early days of HTML there was a fair amount of markup designed to control the look of the page right alongside the content. You might see code like this: 

Hello world!

…all of which is now deprecated due to the aforementioned separation of concerns. 
Which HTML elements are now deprecated?
As of the release of HTML5, use of the following elements is discouraged:
(use instead) (use ) (use CSS font properties, like font-size, font-family, etc.) (use CSS font-size)
(use CSS text-align) (use

    ) (use CSS font properties) (use