title: How to create a customized theme similar to theme_bw in ggplot2?
body: <p>I have the following codes in ggplot2: </p>
  
  <pre><code>require("ggplot2")
  df &lt;- data.frame(x=factor(rep(1:2,5)), y=rnorm(10))
  
  ggplot(df , aes(x,y)) + geom_point(size = 3) + 
  theme(axis.text.x = element_text(angle = 40, hjust = 1, colour = "black", size=12),
        plot.title = element_text(size=16, face="bold", hjust=0.5)) +
  labs(title = "Plot")
  </code></pre>
  
  <p>Now, I want to change the background color to theme_bw, but then the main title and the x-axis options will be changed back to default. </p>
  
  <pre><code>ggplot(df , aes(x,y)) + geom_point(size = 3) + 
  theme(axis.text.x = element_text(angle = 40, hjust = 1, colour = "black", size=12),
        plot.title = element_text(size=16, face="bold", hjust=0.5)) +
  labs(title = "Plot") + 
  theme_bw()
  </code></pre>
  
  <p>So, how can I change the theme to be the same as theme_bw but without losing other options?</p>
  
  <p>Thanks</p>