Add CSS only in Single Event Pages.

add_css_single_event_pages.php

<?php
/**
 * This function adds specific CSS if the page is a Single Event.
 */
if( tribe_is_event() && is_single() ) {
?>
    <style type="text/css">.header_hor .l-subheader-h, .l-titlebar-h, .l-main-h, .l-section-h, .l-subfooter-h, .w-tabs-section-content-h, .w-blog-post-body {
    max-width: 1140px !important;
    }</style>                                                                                                                                                                                                
<?php 
}