CONTRAST
Learn Hub - 5 Principles of Design
The following website illustrates the principle of contrast.

The contrast between black and white draws the user's attention to the most important parts. Additionlly, the difference in font size helps guide the user.
WHITE SPACE
CXL - 8 Web Design Principles that Still Work in 2020
Ebay is a great example of simplifying content with white space.

With so much content on Ebay's website, it can be easy to overwhelm a user. By using white space, the website is more easily navigated and user friendly
REPITITION
Learn Hub - 5 Principles of Design
Python.org is a great example of utilizing repitition. The following images show the header and footer of the mobile Python page.


As you can see the color scheme of blue and yellow is consistent from the header all the way to the footer.
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