title: making y-axis labels bold in ggplot (x-axis is set bold but y-axis label doesn't change)
body: <p>I am trying to set axis labels and ticks bold in ggplot but y-axis labels is not setting to bold. Please suggest what I should add to the script. Below is a reproducible example. I do need 'atop' command to set y-axis labels string as in the example below.</p>
  
  <p>Thanks in advance. </p>
  
  <pre><code>library(ggplot2)
  
  chart &lt;- ggplot(diamonds, aes(x = table, fill = clarity)) +
  
  geom_histogram() +
  
    scale_x_continuous('Month') + 
  
   scale_y_continuous(expression(atop('ET (W'~m^-2~')')))
  
  chart&lt;-chart+theme(axis.title.y = element_text(colour="grey20",size=20,face="bold"),
       axis.text.x = element_text(colour="grey20",size=20,face="bold"),
       axis.text.y = element_text(colour="grey20",size=20,face="bold"),  
       axis.title.x = element_text(colour="grey20",size=20,face="bold"))  
  
  print(chart)
  </code></pre>