Pure HTML & CSS without using Flexbox

I couldn't view your repository however I have some recommendations regarding your code that could be of interest to you.

HTML

• In order to fix the accessibility issues, you need to replace <div class="container"> with the <main> tag. You'd better use Semantic HTML, and you can also reach more information about it from Semantic HTML and Using Semantic HTML Tags Correctly.

• Each main content needs to start with an h1 element. Your accessibility report states page should contain a level-one heading. So, you need to use one <h1> element in the <main> tag instead of using <h2>, <h3> etc.

CSS

• In order to center it correctly, you can use this style that is flexbox:

body {
   display: flex;
   justify-content: center;
   align-items: center;
   min-height: 100vh;
}

Hope I am helpful. :)

Thanks @ecemgo it worked well with me in HTML feedback, but in CSS advice the body tag styling couldn't be centered by your code, but I got it 😊👌.