title: How to set up tkinter Combobox border color
body: <p>I'm looking for a way to modify tkinter Combobox border color and thickness and cannot find a way how to do it.</p>
  <pre><code>from tkinter import *
  from tkinter import ttk
  
  win = Tk()
  win.geometry(&quot;700x350&quot;)
  
  style= ttk.Style()
  style.theme_use('clam')    # why combobox style works only when theme is used???
  style.configure(&quot;test1.TCombobox&quot;, fieldbackground= &quot;red&quot;)
  #style.configure(&quot;test2.TCombobox&quot;, How to set up border color &amp; thickness???)
  
  label=ttk.Label(win, text= &quot;Select a Car&quot;,
  font= ('Aerial 11'))
  label.pack(pady=30)
  
  cb= ttk.Combobox(win, width= 25, values=[&quot;Honda&quot;, &quot;Hyundai&quot;, &quot;Wolkswagon&quot;, &quot;Tata&quot;, &quot;Renault&quot;, &quot;Ford&quot;, &quot;Chrevolet&quot;, &quot;Suzuki&quot;,&quot;BMW&quot;, &quot;Mercedes&quot;])#, style=&quot;test1.TCombobox&quot;)
  cb.pack()
  
  cb['style'] = &quot;test1.TCombobox&quot;     # I need to be able to set up style after widget is initialized
  
  win.mainloop()
  </code></pre>
  <p>In following code example I'm able to modify background but I cannot find how to modify border. Can someone smarter than me help me fill in test2.TCombobox style for red border with some thickness?</p>
  <p>Second question. Why setting up background stops working when I comment theme???</p>
  <pre><code>style.theme_use('clam')    # why combobox style works only when theme is used???
  </code></pre>
  <p>Edit:
  Second question answer:
  Looks like only setting style enables widget's many styling options (that's how I understand documentation).</p>