title: Box and line in R plot Legend
body: <p>I've done a plot, and have one small problem which drive me crazy with the legend part </p>
  
  <p>I can't find a way to center the box in the legend.</p>
  
  <pre><code>x=seq(-4,4,length=200)
   y=dnorm(x,mean=0.816783035,sd=0.862916258)
   plot(x,y,type="l",lwd=2,col="red" , xlim=c(-4, 4) ,  ylab="probabilitiy", xlab="")
  
  
   #Shaded Area TBR!
   c= -0.211653725
  
  
   x=seq(-4,4,length=200)
   y=dnorm(x,mean=-0.393475584,sd=0.895660247)
   lines(x,y,type="l",lwd=2,col="blue")
  
  
   legend("topright", legend = c('TBR', 'TBF', 'Criterion', 'Hit'), 
                 bty = "n",
                 col = c("green", "blue", "red",NA),
                 lty = c(1,1,1,NA),
                 density=c(0,0,0,10),
                 fill = c("green", "blue", "red","red"),
                 border = c(NA,NA,NA,"red"),
                 )
   abline(v= c)
  
   x1 = seq(c,4, length = 200)
   y1 = dnorm(x1,mean=0.816783035,sd=0.862916258)
  
  polygon(c(c,x1) ,c(0, y1),density= 3, col="red")
  </code></pre>
  
  <p><img src="https://i.stack.imgur.com/XJaqH.jpg" alt="enter image description here"></p>