custom navigation menu sela theme

hello, I have already tried to follow the directions in a post to change the color of the navigation menu of the theme sela, but did not succeeded.
I created a child theme, and tried to change the style.css either through FTP or through a plugin recommended in the guide, entering the code css indicated, but it does not work.
css code is introduced:

/* .main-navigation {
background-color: #f25f70;
border-bottom: 2px solid #f25f70;
color: #fff;
display: block;
padding: 0 1em;
} */

below the address of the temporary domain of my site just started:
635.c00.myftpupload.com.
how can I do?
thank you very much!