When explaining advanced CSS techniques for modern web design to a young audience, it’s essential to keep the conversation engaging, relatable, and straightforward. Here’s a way you could approach it:

1. Use Analogies and Simple Language: Compare CSS elements to things they are familiar with. For example, you could liken CSS to the rules of a game, where each rule determines how a part of a website looks and behaves.
2. Focus on Visual Elements: Young people often respond well to visual learning. Show examples of how CSS can change the look and feel of a website. For instance, demonstrate how changing a few lines of CSS code can alter the color, size, or layout of a webpage.
3. Interactive Learning: Use interactive tools or websites where they can see the immediate impact of CSS changes. This hands-on approach can make learning more engaging and memorable.
4. Relate to Their Interests: If they are interested in a particular hobby, sport, or game, show them how CSS can be used to create a website related to that interest. For example, if they like a particular sport, you could show them how to design a sports-themed webpage using CSS.
5. Encourage Creativity: Let them experiment with CSS to create their own designs. This could be as simple as changing the background color of a page or as complex as creating a grid layout.
6. Simplify Complex Concepts: Break down complex CSS concepts into smaller, more manageable parts. For example, when discussing responsive design, start with the basic idea of making a website look good on both a phone and a computer, before delving into media queries.
7. Use Stories and Scenarios: Explain how CSS is used in real-world scenarios. For instance, tell a story of how a website designer used CSS to solve a specific design problem.
8. Patience and Encouragement: Learning something as complex as CSS can be challenging. Encourage them to keep trying and reassure them that it’s okay to make mistakes and learn from them.

Remember, the goal is to spark interest and understanding, rather than overwhelming them with technical details. Tailor your explanations to their age, interests, and level of understanding.