C# Error: 'ExtentReports' is a namespace but is used like a type

Question

Getting error while typing public ExtentReports ext

using NUnit.Framework;
using AventStack.ExtentReports;

using AventStack.ExtentReports.Reporter;


namespace TestProject1.BaseClass
{
[TestFixture]
public class BaseTest
{
    public IWebDriver driver;
    public ExtentReports ext; //shows error here
}
}

also tried : using AventStack.ExtentReports;