I am trying to make it BOX width to 100% but it is not working…

I knew how to use sx prop to change but i dont know why it is not working this time …

here is my code

   <Box width={100} sx={{ border: "2px solid grey" }}>   

width is applied well but when i move width code to sx prop like this 

 <Box sx={{ border: "2px solid grey",width:"100%" }}> 


it is not working ... except width, other prop is working good such as background 
  

this screenshot is make sure that parent’s container width is full with border line

enter image description here

Could you please help me ??

I want box container width change to full