- Split snippets.md into lua-snippets.md, css-snippets.md, imgui-snippets.md, cef-snippets.md

- Added common variables to css-snippets.md
- Added common ImGui functions to imgui-snippets.md
- Added alternatively-styled content tabs to extension list in mkdocs.yml
- Created basic ImGui tutorial in imgui-window-tutorial.md (formerly imgui-windows.md)
- Fixed indentation error in lua-snippets.md

docs/en/beamng/imgui-snippets.md

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+!!! warning "This site is under construction!"
+
+    This site is being actively worked on. 
+    
+    Feel you could help? Please do by clicking on the page with a pencil on the right!
+
+    This can be done any page too.
+    
+# BeamNG.drive ImGui Code Snippets
+
+## Setup
+
+### Setup ImGui
+
+```lua
+local im = ui_imgui
+```
+
+### Setup Window
+
+```lua
+im.SetNextWindowSize(im.ImVec2(366, 100), im.Cond_FirstUseEver)
+```
+
+### Create window
+
+```lua
+im.Begin("Window Title") -- Create window
+im.End()
+```
+
+## General
+
+=== Basic Formatting
+
+	```lua
+	im.Text("")
+	im.TextWrapped("") -- automatic word wrap
+	im.TextColored(im.ImVec4(0,1,0,1), "") -- R,G,B,A
+	im.TextDisabled("") -- predefined style for disabled text
+
+	im.LabelText("", "")
+	im.BulletText("") -- Bullet point with text
+	im.SeparatorText("") -- Separator with centered text
+
+	im.Separator() -- might want a NewLine before these
+	im.SameLine() -- horizontally append the following element to the previous element
+	im.NewLine()
+
+	im.Spacing() -- small padding
+	im.Indent()
+	im.Unindent()
+	```
+
+=== Inputs
+
+	```lua
+	im.Button("", im.ImVec2(0,0)) -- 0 = fit to content
+	im.SmallButton("") -- Fit to content and slightly less padding
+	im.ArrowButton("", 0) -- arg 1: string is not actually used? arg 2: 0 = left, 1 = right, 2 = up, 3 = down
+	im.InvisibleButton("", im.ImVec2(0,0), ...) -- used for imgui cursor positioning?
+
+	im.Checkbox("", im.BoolPtr(false))
+
+	im.RadioButton1("", im.BoolPtr(false))
+	im.RadioButton2("", im.IntPtr(), 0) -- arg. 3: 0 or 1 for disabled or enabled
+	```
+
+=== Other
+
+	```lua
+	im.Bullet()
+
+	im.ProgressBar(0.5, im.ImVec2(0,0), "") -- arg 2: 0 for default width and/or height
+
+	im.TextUnformatted("", "") -- Second argument seems to crash the game
+	```