title: Add Limit Lines to D3.js Line Graph
body: <p>Hi. Is there a way to put a limit line for a d3js line graph? means a limit line along x axis which shows the maximum limit!</p>
  
  <pre><code>svg.append( "line" )
  .attr("x1", x( x.domain()[0] ) )
  .attr("y1", y( 80 ) )   // whatever the y-val should be
  </code></pre>
  
  <p>This is the code I have used rightnow.but not working.having doubt with the css part</p>
  
  <p>Can anyone please give me a detailed overview?</p>