Think of HTML as the bony 💀 framework/skeletal system, and CSS as the Flesh, the Clothes, the Colorful Bags, Shoes, Hair, and the likes.
You can add styles to your page in 3 ways
1.inline -> adding style attribute to your html tags
E.g <h1 style="color: #fff">hello </h1>
2.internal-> adding style tag in head
3. External-> create another file with extension .css and access html tags there to add styles and link this file in your html.
Brother, After 2 or 3 months, you will read your question and you will laugh at yourself. Because these two are really dependent on each other. Web designer is not a web designer if he or she doesn't know HTML and CSS. Keep learning and you will find your way 😊👍