below these three code snippets which one would be the best one to implement in a style sheet ?
*{
box-sizing:border-box;
margin:0;
padding:0;
}
html,body
{
box-sizing:border-box;
margin:0;
padding:0;
}
html
{
box-sizing:border-box;
margin:0;
padding:0;
}
The asterisk selector * applies to all elements, not just the html/body element. You should avoid this, since you could be writing rules for a div later on and you wouldn't be able to give it any margin or padding (or change its box-sizing)! Use either the 2nd or 3rd snippet depending on whether you want to give the body any margin or padding.