See the style-guide.md file for the colors used in the design. It also contains the font-size values and font types used in the design.
If you get stuck, there is a YouTube channel called Kevin Powel. You may need to watch how he builds this project and his tutorials and tricks about CSS.
I do recommend you watch this video. It will help you to understand what basic mistakes you made like using specific values for width and height.
I also recommend Conquering Responsive Layout free course by Kevin. It helped me to understand the core concepts of responsiveness in web pages and the basics of CSS.
If you have any further questions, don't hesitate to ask.
If you find my feedback helpful, don't forget to mark it useful ^_^