What would be the best way to develop CSS3 styles? [closed]

I have always designed my CSS3 code:

/*

Author : 3lmo

Date : 13/NOV/2017

*/




      body {

        margin:0;
        padding: 0;


       }

    h1,h2,h3,h4,h5,h6 {


       font-family: arial;
       font-size:100%;
    }



    .contenedor {

        margin:0 auto;
        width:50%;
        text-align:justify;
    }

    .text-center{

        text-align:center;
        font-family: arial;

    }

and my question is what is the best pattern, method or design to develop CSS3 code (styles), more organized or standard in the W3 I searched and found nothing similar?

Is there something similar like that in CSS3?