How to Use CSS to implement the triangle effect and css to implement the triangle

How to Use CSS to implement the triangle effect and css to implement the triangle

How to Use CSS to achieve triangle effect:
Suggestion: writing code as much as possible can effectively improve learning efficiency and depth.
Sometimes we often find that some rectangles have a triangle effect somewhere, which is amazing. Of course, you can use a background image. Here we will briefly describe the effect of not using a background image. The Code is as follows:

<! DOCTYPE html> 
The principle is very simple. The above Code may not be obvious enough. You can see the following code example at a glance.
<! DOCTYPE html> 
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