Hi Kate,

 There is no "general" default button for appearance, yet there are ways to set
the look you want.
Right click an empty area on the desktop.
In the popup menu click Properties.
Click the Appearance tab.
Click the dropdown listbox arrow for "Windows and buttons" and select either
Classic or XP style.
Click the dropdown listbox arrow for "Color scheme" and select either Windows
Standard or Classic.
Click Apply.
Click the Advanced button.
Click the dropdown listbox arrow for "Item".
Click on an item in the list that you want to change the configuration for.
If available, change the items size and or color(s).
If available, change the font, size and color.
When you're finished making any changes to any/all items, click Ok.
Click Apply > Ok.

 **Note:  Do not click Apply if you are not satisfied with the configuration,
if you do and you do not like the look you will have to go back and reconfigure
the settings.

 Also, if you wish, clicking on different areas in the upper pane of the
advanced appearance window will select an item the same as if you use the
dropdown list.

There is no default but...
Right click an empty area on the desktop.
In the popup menu click Properties.
Click the Appearance tab.
Pick a theme.  It will reset to some 'decent' settings.  Maybe you can
use it as a starting point, then tweak a few of them?    I always did
that when I was young and energetic.   I just take what comes with the
initial load now.   I used to change fonts, sizes, etc. all the time.
Just don't find it worth the time now.  I'm more interested in
production or using the PC.

No implication intended.

Use my free Desktop Reset Tool. Download it here
http://pcbutts1.com/downloads/tools/tools.htm

Hi Kate,

Try using a native XP Theme.