How to change the content width using php?

I've created a custom template using php and would like to know how to modify the content width? Do I have to create a class within php and then modify the width using CSS?

This is how my php template looks right now:

?php /* Template Name: NewEventTemplate */ ?

?php
/**
* The template for displaying pages.
*
* @package Salient WordPress Theme
* @version 10.5
*/

// Exit if accessed directly.
if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

get_header();
nectar_page_header( $post-ID );
$nectar_fp_options = nectar_get_full_page_options();
?  

div class="container-wrap"
    div class="?php if ( $nectar_fp_options['page_full_screen_rows'] !== 'on' ) { echo 'container'; } ? main-content"
        div class="row"
            /div
              header class="entry-header"
             ?php the_post(); ?
    h1 class="entry-title"?php the_title(); ?/h1
  /header

            ?php

            nectar_hook_before_content(); 
        the_content();

            if ( have_posts() ) :
                while ( have_posts() ) :
                    the_post(); 
                    the_content();

                endwhile;
            endif;

            nectar_hook_after_content();

            ?
        /div!--/row--
    /div!--/container--
/div!--/container-wrap--

?php get_footer(); ?