The documentation is lacking a lot of information, but the following works here:
from tkinter import *
from tkinter.ttk import *
app = Tk()
style = Style()
style.element_create('Fruitsalad.Horizontal.Scrollbar.trough', 'from', 'default')
style.element_create('Fruitsalad.Horizontal.Scrollbar.thumb', 'from', 'default')
style.element_create('Fruitsalad.Horizontal.Scrollbar.leftarrow', 'from', 'default')
style.element_create('Fruitsalad.Horizontal.Scrollbar.rightarrow', 'from', 'default')
style.element_create('Fruitsalad.Horizontal.Scrollbar.grip', 'from', 'default')
style.layout('Fruitsalad.Horizontal.TScrollbar',
[
('Fruitsalad.Horizontal.Scrollbar.trough', {'children':
[('Fruitsalad.Horizontal.Scrollbar.leftarrow', {'side': 'left', 'sticky': ''}),
('Fruitsalad.Horizontal.Scrollbar.rightarrow', {'side': 'right', 'sticky': ''}),
('Fruitsalad.Horizontal.Scrollbar.thumb', {'unit': '1', 'children':
[('Fruitsalad.Horizontal.Scrollbar.grip', {'sticky': ''})],
'sticky': 'nswe'})],
'sticky': 'we'}),
])
style.configure('Fruitsalad.Horizontal.TScrollbar',
troughcolor='green',
background='red',
arrowcolor='white')
style.map('Fruitsalad.Horizontal.TScrollbar',
background=[('pressed', '!disabled', 'pink'), ('active', 'orange')])
scrollbar = Scrollbar(app, orient='horizontal', style='Fruitsalad.Horizontal.TScrollbar')
scrollbar.place(width=150)
scrollbar.set(0.0, 0.5)
app.mainloop()
