If you have a sticky header (Position fixed header on the top of the html page), your anchor link with CSS ID would not work as you expected. The target section would be covered by the position fixed header.

You can use the following CSS to offset the fixed header height.

/* The target CSS ID with :before pseudo class */
.offset:before { 
  display: block; 
  content: " "; 
  height: 150px;      /* Give height of your fixed element */
  margin-top: -150px; /* Give negative margin of your fixed element */    
  visibility: hidden; 
}

Done =)

Reference: Offsetting Anchor Hash Tag Links To Adjust For Fixed Header