There isn't one perfect way to design things since our needs are different. A relative of mine has failing eyesight and requires high contrast - while I am quite sensitive to bright lights and need to dim my screens beyond what most people find workable.

The best lesson in accessibility to learn is that our societal needs are complex and the various standards exist for good reason. If you want to create a complex and particular design using CSS that is fine but keep the tagging underlying that design compatible with screen-readers and allow easy overriding of styling.

One of the most frustrating things for accessibility is advertising since it specifically goes to lengths to use obfuscated class names (to avoid ad-blocks) and bright colors (often via images/videos that contain embedded text). At some point I really do hope we realize just how expensive advertising is and how many externalized costs it forces on us all.