That's not correct CSS syntax. Correct would be:
table{
position:absolute;
top:-100px;
left:90px;
margin:300px;
background-color:#000000;
}
table a:link {text-decoration:none;}
table a:visited {text-decoration:none;}
table a:hover {background-color:Green;}
table a:active {text-decoration:underline;}
If you want to nest CSS rules using the syntax in your question, you can use an alternate stylesheet language that compiles to CSS like LESS or SASS.