The Value of Minimal CSS Frameworks
There are frameworks that let you build good-looking web pages with plain HTML and no CSS. By using such a framework, you save the effort of writing CSS, which improves development efficiency. The design is also unified, so you end up with good-looking web pages. Since you use semantic HTML, you can write meaningful markup.

Compared to HTML made up of divs and CSS, using semantic HTML lets you write meaningful markup. This improves accessibility and also helps with SEO.
Introducing the Frameworks
Here are some minimal CSS frameworks I recommend.
simple.css
simple.css is my personal top pick among minimal CSS frameworks.

pico

There are various other samples, so take a look.

Summary
I introduced minimal CSS frameworks that let you build good-looking web pages without writing CSS. They improve development efficiency and unify the design, so I recommend them for building web pages. If you have a framework you recommend, please let me know!