Changing CSS properties from JavaScript can be great fun .

Pressing the first button...

changes body style properties...

and the text boxes' colours.

Clicking the second button...

changes body style properties.

And some of the div,...

plus it moves it to the lower right corner of the window.

CSS names versus JavaScript names :


font-family - fontFamily
font-size - fontSize
margin-left - marginLeft
etc.

Often it's more practical to change entire classes,...

as we do ....

when the third button is pressed.

'return' means 'nothing left to do here, leave this function now'.

If the program reaches these lines, that means the 4th button was pressed.

Important this one, for it shows how you can change a tag's contents from JavaScript.