I don't think you can change the default page and text colours for Chrome without using an extension that styles the pages. I don't use it, so can't advise anymore than that. If you switch browsers to Firefox you can set default page and text colours. But with any web browser the default page colours only show if the web page has not set its own colours. So, an extension like Stylish is necessary to override the website code.
Word can also be set to use a different colour by editing and saving the Normal template, but it won't affect any docs that don't use the Normal template. Excel is more complicated...
However, I think Word and Excel will default to the colour you set in a custom theme.
Follow 'Option Two' in this tutorial to create a custom Windows theme: Get colored title bars in Windows 10
When you get to step 7, editing the windows.theme file, add the following lines:
That will set the default window colour. 200 200 200 is the grey in the screenshots I posted earlier.
Window=200 200 200
255 255 255 is white.
0 0 0 is black.
225 225 225 is a lighter grey.
175 175 175 is a darker grey.
So, adjust these values to the colour you want.