How to overwrite on responsive.css

Hello, I recently downloaded the catch-everest theme. I created a child theme. I just want to make several minor changes (line-spacing, color, ...), so i want to use my new "style.css" to do that. But I have a problem: the responsive.css page from the parent theme overwrites my new style.css page. For example : I changed the margin-bottom from this line in responsive.css, that i copy/pasted in style.css: "article.sticky .featured-post, .page-header, p, .featured-image, .entry-content table, .comment-content table, .widget.widget_catcheverest_social_widget, #content .searchform", but it doesn't change anything. How can i fix that ? I would like to have only one style sheet to configure and I would like to keep the responsive design. Thank you !