Some help needed with ID Selectors


Okay, so the task requires me to add an ID selector for the ID "header-text", and no matter where I put the line of code in, it just won't work. Here's a segment of the code:
.header {
background-image: url("");
background-position: center center;
background-size: cover;
height: 700px;
width: 100%;

/* Add the ID selector to this CSS rule */

margin: 0 auto;
position: relative;
text-align: center;
top: 25%;
width: 60%;

h1 {
color: #FFF;
font-family: 'Quicksand', sans-serif;
font-size: 70px;
font-weight: 400;
line-height: 60px;
margin: 0;

ID Selectors: CSS


The above is a declaration block with no selector.


#selector {