import { loadStyle } from 'lightning/platformResourceLoader';
import styles from '@salesforce/resourceUrl/prueba';

renderedCallback() {
         Promise.all([
             loadStyle(this, styles + "/main.css")
         ]).then(() => {
             console.log('Files loaded.');
         }).catch(error => {
             console.log("Error "+error.body.message);
         });

     }