title: Replicate the style of tisPlot in ggplot2
body: <p>I want to replicate the style of tisPlot, from the tis package, in ggplot2. I am having trouble creating the line segments capping both the left and right y-axes in ggplot2. I have attached example code that shows a basic tisPlot along with what I have done to match that style in ggplot2. Does anyone here know how to solve this last part of the problem, namely, adding line segments at the tops of the y-axes? Thanks. </p>
  
  <pre><code>library(tis)
  library(tidyverse)
  library(lubridate)
  
  set.seed(5)
  
  # make example time-series data
  firstTis &lt;- tis(cumsum(rnorm(120)), start = c(1996, 1), freq = 12)
  
  tisPlot(firstTis)
  
  # put example times-series data into a dataframe
  df &lt;- data_frame(
    date = firstTis %&gt;% time() %&gt;% date_decimal() %&gt;% date(),  
    firstTis = firstTis %&gt;% as.numeric()
    ) 
  
  ggplot(df) +
    geom_line(aes(x = date, y = firstTis)) +
    theme_classic() + 
    theme(
      axis.ticks.length = unit(- 7, "pt"),                                               
      axis.text.x = element_text(margin = margin(t = 10, b = 0, unit = 
  "pt")),
  axis.text.y = element_text(margin = margin(r = 10, l = 0, unit = "pt"), 
  color = "white"),     
  axis.text.y.right = element_text(margin = margin(r = 0,  l = 10, unit = 
  "pt"), color = "black")
  ) +   
  scale_y_continuous(sec.axis = dup_axis(name = "")) +
  </code></pre>