What does a negative value of margin mean?

HTML:

<div class="main">
  <div class="inner"></div>
</div>
 

CSS:

*{
  padding: 0;
  margin: 0;
}
.main{
  margin: 40px auto;
   width: 100px;
  border: 1px solid -sharp000;
}
.inner{
 width: 100px;
 height: 100px;
 background-color: pink;

/* margin-top: -10px;
 margin-top: 10px;
 margin-bottom: -10px;
 margin-bottom: 10px;
 margin-left: -10px;
 margin-left: 10px;
margin-right: -10px;
margin-right: 10px;*/
}

in the above inner comments, the positive and negative values of margin-top, margin-bottom and margin-left all have an effect, but the positive and negative values of margin-right do not reflect. Why? And is the point of setting negative values just for movement?

Css
Sep.16,2021

the negative effects of upper left and lower right are not the same

https://codeshelper.com/a/11.

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