You need 4 Panels.
button_open
button_open_hover
button_close
button_close_hover

button_open (OnLoad):
self:RegisterEvent("PLAYER_ENTERING_WORLD")

button_open (OnEvent):
BT4Bar2:Show()
BT4Bar2:SetAlpha(0)
local button1 = kgPanels:FetchFrame("button_open_hover")
button1:Hide()

button_open (OnEnter):
self:Hide()
local button1 = kgPanels:FetchFrame("button_open_hover")
button1:Show()

button_open_hover (On Leave):
self:Hide()
local button1 = kgPanels:FetchFrame("button_open")
button1:Show()

The Hover-effect should now work.

button_open_hover (OnClick):
self:Hide()
local button1 = kgPanels:FetchFrame("button_close")
button1:Show()
local button2 = kgPanels:FetchFrame("button_open")
button2:Hide()
local button3 = kgPanels:FetchFrame("button_open_hover")
button3:Hide()
BT4Bar2:SetAlpha(1)

The Open Buttons disappear und now you can see the BartenderBar + button_close.

button_close (On Enter):
self:Hide()
local button1 = kgPanels:FetchFrame("button_close_hover")
button1:Show()

button_close_hover (OnLeave):
self:Hide()
local button1 = kgPanels:FetchFrame("button_close")
button1:Show()

So the Hover-effect should now work...

button_close_hover (OnClick):
self:Hide()
local button1 = kgPanels:FetchFrame("button_close")
button1:Hide()
local button2 = kgPanels:FetchFrame("button_close_hover")
button2:Hide()
local button3 = kgPanels:FetchFrame("button_open")
button3:Show()
BT4Bar2:SetAlpha(0)


So... the sidebar should be done...
There is just one problem... when you set the alpha 0, the bar is invisible but still there.. you can click the buttons on the bar when clicking an the position the buttons are..

so you have to make a transparent panel that should appear above the bar when the bar is hide.

for example:
sidebar_cover
Intercept Mouse Clicks: YES
BackGroundColor: 0% Opacity
NoBorder....
Strata: Medium
Level: 5

button_close_hover (OnClick):
Add the Line:
local sidebar = kgPanels:FetchFrame("sidebar_cover")
sidebar:Show()

button_open_hover (OnClick):
Add the Line:
local sidebar = kgPanels:FetchFrame("sidebar_cover")
sidebar:Hide()


Enjoy!