White background hurt my eyes. Only keywords coloring is not enough for code coloring.

Tidy Up is great function but I've noticed that if I'm working on a Saved code and I hit that button, the code formats and then my save button disappears..

Support for System.Diagnostics.Debug.Assert could be added. Given that it's an internal verification system that fails when the assertion is incorrect, it could be helpful to at least throw a message in the output window when an assertion wasn't working

Would be great to have this as a PWA

Collaboration doesn't work at all.
I clicked 'collaborate' and sent the link to other machine. I opened it in broswer and clicked 'yes, join' But I don't see collaborator in the host and in the remote machine. I don't see the changes was made.Nothing

when we write a code also we need to debug , it is useful to resolve issue very fast.

Console.WriteLine($"{i} ");

throws error: Compilation error : Unexpected character '$'

Provide a method to store environment variables per our account that couldn't be seen by anyone we shared the code with.

Make them accessible in code with this: https://docs.microsoft.com/en-us/dotnet/api/system.environment.getenvironmentvariable.

In CodePen, you can show the HTML, CSS, and JS on one half of the iframe and the result on the other half, as well as open and close them by clicking on tabs located at the top of the iframe. It would be awesome if we could have the code be on one tab, and the console output on the other tab

Make it so that the code can not be altered, just viewed

There exists five redundant horizontal tabs 0x09 at the second line of all C# templates (Framework, Core, and Roslyn). They have existed for at least a year now.
I am hoping they can be removed.
Thanks.

Now that Blazor server-side has been released and client-side in preview (due to be released with .Net 5 in November), you should think about supporting the project type on .Net Fiddle

If you move the cursor to the opening tag highlight the closer tag

Any plans to support an Azure Function like interface with files area for run.csx, function.json?

Lots of C# developers out there who can't afford to have an Azure Tenant that can help collaborate on our projects.

https://dotnetfiddle.net/jsV9f5

View IL feature doesn't work.

The same code gives different results in .NET Framework 4.7.2 & .NET Core 3.1

    var testValues = new string[] { "0", "+2", "-2", "+-" };


    Console.WriteLine(string.Join(", ", testValues.OrderBy(sv => sv)));

On .NET Core, you cannot do Console.ReadLine() as it doesn't work on that platform for some reason

Support MyGet as a source for nuget packages, example:
// @myget: mypackage -Version 2.7.0

Such as 'Def.1.1.1', which I successfully referenced but could not use.

The error is:

Compilation error (line 13, col 21): The name 'Def' does not exist in the current context.

The site shows that the package is "on disk", but '/usr/nugetCache/def' does not contain 1.1.1.

Is there a problem?