Add default values to styles

[veredcon]

In the original webview toolkit there were default styles configured in case no VSCode variable is present.
for example in case of color
This helps in local development when there are no VSCode variables available.. otherwise styles look bad

e.g:
button in local development:

button as part of vscode weview:

[bendera]

That's a valid point. Until I add them, you can use these css variables during the development:
https://github.com/vscode-elements/elements/blob/main/dev-assets/dark-v2.txt
This is the default theme called "Dark Modern".

[bendera]

Look at this: https://github.com/vscode-elements/webview-playground

[bendera]

To anyone who wants to pick up this task,

This is a chore but easy task. You have to add a fallback value in every place where a --vscode prefixed css variable is used. The default VSCode the is the "Dark Modern". This file contains all the theme variables provided by this theme. Keep in mind that --vscode-editor-font-family and --vscode-font-family are platform dependent, sans-serif and monospace will work well for them.