how to edit horizontal line length html

1<!-- HTML -->
2
3<!-- You can change the style of the horizontal line like this: --> 
4
5<hr style="width:50%", size="3", color=black>  
6
7
8<!-- Or like this: -->
9
10<hr style="height:2px; width:50%; border-width:0; color:red; background-color:red">
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12

1<hr style="height:2px; width:50%; border-width:0; color:red; background-color:red">