You will not lose your custom css codes because they are saved in the database.
At the moment you do not need a child theme, because I am modifying your Evolve Plus theme code.
I cannot find what is causing this issue. Why it works on my localhost and our demo site but does not work on your website. The codes are the same in version 1.7.5 and 1.9.0, only location is different (found in different file). Therefore, I think it could be a bug with the theme’s excerpt trimming function, but at the moment, I do not know the factor or how to reproduce it on my localhost.
I had go ahead and made 2 modifications on your website. I am listing it down here as a record.
1) Theme version 1.7.5
2) evolve-plus/library/functions/basic-functions.php at line 377 to 380 (within function t4p_content), commented out original codes and use WordPress core function wp_trim_words.
//mod by denzel, use WordPress core function wp_trim_words()
//$content = apply_filters('the_content', $content);
//$content = str_replace(']]>', ']]>', $content);
$content = wp_trim_words($content,$limit);
3) navigation.php at line 12 to 13
<div class="col-sm-6 col-md-6 nav-previous"><?php previous_post_link( '%link', '<div class="btn btn-left icon-arrow-left icon-big">%title</div>',true ); //mod by denzel, add $in_same_term = true ?></div>
<div class="col-sm-6 col-md-6 nav-next"><?php next_post_link( '%link', '<div class="btn btn-right icon-arrow-right icon-big">%title</div>',true );//mod by denzel, add $in_same_term = true ?></div>
Now your excerpt length works, as well as the previous and next posts will link to those within the same categories as a priority.
In the future, if you need to re-apply these modifications, you can look for me and show me the url to this forum thread.
Hope you understand that these modifications are done out of goodwill and for this issue only.
Sorry for causing inconveniences.