CSS for first td of each tr in certain table

Your this code is not correct:

{ width: 0px; important; }

this should be:

#student > tr > td:first-child{ 
  width: 0px !important; 
}

before important property you are using semicolon which is not correct.

 #student > tr > td:first-child{
  display : none;
    }

Use the below.

table#student tr td:first-child{display:none;}

WORKING DEMO

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