Your HTML website is very bland looking. No offense. That’s why the creators of the web created CSS, cascading style sheets. CSS is what makes your website prettier than a text file. It’s a tool to make your website visually appealing. It gives you incredible control over every little detail of your website’s design, but that means you’ll need a lot of CSS to control every little detail of your design. Otherwise, your website will end up looking like a slightly better looking text document. Unfortunately, you can’t just add a little bit of CSS and have a beautiful website. Having such fine control is a blessing and a curse. Very few things happen automatically.
So, what can CSS do exactly? Take a look at any website. Every single little thing related to design is controlled with CSS. The position of the logo. The size of the logo. The menu. The color of the menu text. The fade effects. The position of the menu text in relation to everything else. Every. Little. Detail.
There are two different ways you can add CSS to your website. You can embed CSS directly into your HTML. In that case, the deployment process would be exactly the same, or you can also put all of your CSS in an external file and link that file to your HTML file. In that case, you would have to upload two files to your server.
My guess is that there are millions of HTML & CSS websites out there. They’re more common than HTML websites. All you really need to have a nice-looking website is HTML & CSS.