Lesson 6: CSS foundations and cascade: Real-world case study

Concept Explanation

This lesson moves from isolated practice to a small, realistic interface problem. You will style a theme switch for a card-like layout using custom properties so one change updates several parts of the design at once. The focus is not on making something flashy, but on organizing styles in a way that feels practical: readable variables, clear component rules, and predictable overrides. By working through a realistic example, you will see how the cascade supports reusable design decisions instead of becoming a source of confusion.

Where to Put the Code

1. Start with variables and inputs. Place style rules in reusable class selectors.
2. Add processing logic in the middle section.
3. Finish with output and quick validation.

Command Reference

• Identify which values should change between themes and place only those in custom properties.
• Test the component in both light and dark modes to confirm text and background still work together.
• Adjust one token, such as accent color or spacing, and observe how many places update automatically.
• Explain one reason this setup is more practical than duplicating the full component rules for each theme.

Step-by-step Guide

1. Start with the base variables and confirm the light theme looks correct.
2. Add the theme modifier class and check which properties change through the cascade.
3. Style the component using variables instead of hard-coded colors where possible.
4. Modify one theme value, such as the accent color, and compare the result before and after.
5. Review the final structure and make sure the component rules stay separate from the theme rules.

Practice Exercises

• Create a second component, such as a button or badge, that reuses the same theme variables.
• Add a muted text token and apply it to supporting text inside the card.
• Build a variation that uses the same theme system but a different accent color for warnings.

Coding Challenges

• Scale the theme setup to support multiple components without copying full rule sets.
• Keep the theme rules easy to override while avoiding confusing selector chains.

Mini Practice Tasks

• Add one new design token for spacing or color.
• Rename one class to better reflect its job.
• Describe in one line what problem custom properties solve in this example.