Unable to resolve service for type 'microsoft.entityframeworkcore.dbcontextoptions

using Microsoft.EntityFrameworkCore;

namespace WebApi.Model
{
    public class EmployeeContext : DbContext // Inherit
    {
        // Constructor
#pragma warning disable CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
        public EmployeeContext(DbContextOptions<employeecontext> options) : base(options) // DI
#pragma warning restore CS8618 // Non-nullable field must contain a non-null value when exiting constructor. Consider declaring as nullable.
        {
            
        }

        // DataSet Property of the Classes
        public DbSet<tblemployee> TblEmployee { get; set; }
        public DbSet<tbldesignation> TblDesignation { get; set; }

    }
}

using Microsoft.EntityFrameworkCore;
using WebApi.Model;

namespace WebApi
{
    public class Startup
    {
        public Startup(IConfiguration configuration)
        {
            Configuration = configuration;
        }
        public IConfiguration Configuration { get; }
        public void ConfigureServices(IServiceCollection services)
        {
            services.AddControllers();
            services.AddDbContext<employeecontext>(db => db.UseSqlServer(Configuration.GetConnectionString("ConEmp")));
        }

        public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
        {
            if(env.IsDevelopment())
            {
                app.UseDeveloperExceptionPage();
            }
            app.UseHttpsRedirection();
            app.UseRouting();
            app.UseAuthorization();
            app.UseEndpoints(endpoints =>
            {
                endpoints.MapControllers();
            });
        }
    }
}