css图片不居中的原因

$.ajax({
           url: "/api/student/poststudent",
           type: 'POST',
           data:JSON.stringify({ name: "张三", age: 21 }),
           success:function () {
           },
           dataType: "json",
           contentType: "application/json"
       });

    public class Student
    {
        public string Name { get; set; }
        public int Age { get; set; }
    }

[HttpPost("{id}")]
public void PostStudent(Student student)
{
}

[HttpPost("{id}")]
public void PostStudent(dynamic student)
{
    var name = student.name;//name大小写与前端参数一致
    var age = student.age;
}

[HttpPost("{id}")]
public void PostStudent(JObject student)
{
}

$.ajax({
           url: "/api/student/poststudent",
           type: 'POST',
           data:'"name=张三,age=21"',//这里是重点！用单引号包一个双引号，双引号里为字符串内容！
           success:function () {
           },
           dataType: "json",
           contentType: "application/json"
       });

[HttpPost("{id}")]
public void PostStudent([FromBody] string values)
{
}

//允许一个或多个来源可以跨域
services.AddCors(options =>
{
      options.AddPolicy("CustomCorsPolicy", policy =>
      {
             // 设定允许跨域的来源，有多个可以用','隔开
             policy.WithOrigins("https://localhost:5000")//只允许https://localhost:5000来源允许跨域
             .AllowAnyHeader()
             .AllowAnyMethod()
             .AllowCredentials();
      });
});

app.UseCors("CustomCorsPolicy");