title: put legend of area chart inside the figure
body: <p>here is my data and my area chart:</p>
  <pre><code>df&lt;- data.frame(age=15:40,h1= 25:50,h2=35:60,h3=45:70)
  data1&lt;- df %&gt;% gather(timeuse, minute, -age)
  
  ggplot(data1, aes(x = age, y = minute, fill = timeuse)) +
    geom_area() +
    scale_fill_brewer(palette = &quot;Gray&quot;)+
    scale_x_continuous(breaks = seq(15, 90, by = 5))+ 
    scale_y_continuous(breaks = seq(0, 1500, by = 100))+
    theme_classic() 
  </code></pre>
  <p>I want to put legend inside the area chart like this picture:</p>
  <p><a href="https://i.stack.imgur.com/YQKBL.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/YQKBL.png" alt="enter image description here" /></a></p>