I want to make my code better [for search engines]

A new plugin should be used soon to allow auto-translation, but already and although old, by using translate or deepl, you can glean some additional information to what has been said by @Jon Fritz , @Ben M and @B i r n o u ... by reading some posts https://www.puce-et-media.com/category/structure-et-contenu/referencement/

I don't really agree with the idea of having to pay to place a meaningful SERP.

Of course, all things considered, depending on the sector of activity in which the site operates ... real estate, finance, trade, in short, growth markets ... the task will be harder, and will require a more experienced knowledge... but this is not unattainable

Let's take a simple example of what I mean, and I would like you all to contribute to it... let's take an article on accessibility ... sorry it is written in French and so probably the demo won't work from your own country...  https://www.puce-et-media.com/aria-les-bases-roles-reperes-etats-et-proprietes/

This is an article from 2017... so it's quite old... and as I said it's in French which may cause some trouble if you are based in Australia, the United States or even Europe, but not in France...anyway... I will give snapshots

Let's put ourselves in the shoes of a person who is looking for information on the aria-checked and/or aria-pressed state or properties. (I agree it's a tiny market, but anyhow Dubreq, Waddingtone, FX Schmid puzzle, doesn't return tons of results on single keywords... so that's more or less the same type of usecase and far under the present exemple.

Dubreq

Waddingtons

FX Schmid Puzzle

aria-checked

So the main point is to try to understand what our content talk about and how it can be helfull to the users for whom it is intended.

It is therefore important, even essential, to ask ourself as a content contributor, how to help the user with this content, and how it can help him.
From this analysis, and with the precious help of Google Trends (among others) https://trends.google.com/trends/,  we will be able to refine the request to enter, or formulate, by the concerned users... which could be for our current example... sorry it's in French 😞

accessibilité états propriétés aria-checked aria-pressed

So here is the verdict... the page comes up :

third on Google,

fifth on Bing

and fifth on Duck Duck Go...

Nothing was paid for... no ads were subscribed... but a mix of what mostly @Jon Fritz  and @Ben M said...

common sense, appropriate content, and I will add a pre analysis of Google Trends ... are all very usefull to get a nice SERP.

All things being equal  -- proper HTML syntax, mobile friendly site, plenty of search-relevant, keyword-rich content, sitemap.xml, etc... -- how much are you spending on Google & Bing ads? 

Little known fact:  Google favors sites that pay for Google Ads, not a lot but a little.  And your site will get indexed quicker with paid ads than it will without them.

In the absence of organic site ranking, the best way to drive new traffic to sites is with paid search ads.  When people search for your targeted keywords, they often see you on page 1 results alongside your competitors.  The higher your ad budget, the more impressions you get.  The lower your ad budget, the fewer impressions you get.  Adjust your ad budget accordingly. 

Your search advertising strategy is important too: 

• Are you getting the greatest return from your investment (ROI)?
  https://support.google.com/google-ads/answer/14090?hl=en
• Are you targeting the best geographic regions and the best keywords based on what people search for?
  https://support.google.com/google-ads/answer/1722043?hl=en
  https://ads.google.com/home/tools/keyword-planner/

The second best thing you can do is post relevant videos on YouTube which Google also indexes. 

Social media comes third.  What you post on Twitter, Facebook, Instagram, etc will drive traffic to your site, particularly if your pages are properly coded with OpenGraph meta tags.

https://ahrefs.com/blog/open-graph-meta-tags/

Hope that helps.

CSS formatting has nothing to do with search engines seeing the content of your page.  Search engines only see the source code.  You need to look into tools like Moz, SEMRush, Ahrefs, etc. to help with your SEO or at the very minimum something like Google Webmaster Tools ( https://search.google.com/search-console/ ).