VS Code - the type or namespace name 'System' could not be found error

I am learning VS Code with .Net Core.

I have installed .Net Core 3.0 SDK.

I have also installed the following extensions in VS Code

• C# ms-vscode.csharp C# for Visual Studio Code (powered by OmniSharp).
• .NET Core Starter's Pack blairleduc.net-core-starters-pack
• C# FixFormat leopotam.csharpfixformat

As you can see in the following image, vs code is showing errors on almost all key words. How can i fix this?

I can do dotnet run without any issue and Hellow World! displays for me.

I have added following to settings.json file by following this https://github.com/OmniSharp/omnisharp-vscode/issues/928

"csharp.suppressDotnetRestoreNotification": true

I have also added the following to the csproj file

<NoWarn>8019</NoWarn>

I have also performed dotnet restore and also performed any suggestions put in front by VS Code. Still no luck fixing this issue.

VS Code version info

Version: 1.39.1 (user setup)Commit: 88f15d17dca836346e787762685a40bb5cce75a8Date: 2019-10-10T23:31:28.683ZElectron: 4.2.10Chrome: 69.0.3497.128Node.js: 10.11.0V8: 6.9.427.31-electron.0OS: Windows_NT x64 10.0.17763