Child-theme: a new entry in Style.css doesn’t work

Dear all, I have installed Evolution Pro since 4 years and during this time I have periodically customized the site using style.css located in ../wp-content/themes/catch-evolution-pro/ without any problems (supported by CSS-customize plugin). More than a year after the last time, i had to do a little customization, namely, hidden a frame of a new inserted search-field. I did in the past this operation more times adding the code in style.css. For your information the code is: #woocommerce_product_search-3.widget.woocommerce.widget_product_search { border-style: hidden; } Very simple statement but now it doesn't work. If I add this code using WP-tool "Appearance" -> "Customizing" -> "Additional CSS", then it works correctly. It is not a "capital problem" but could you please help me to undestand why it does that? I cannot solve this issue myself. My setup: WP-Version: 5.5.3 Catch Evolution Pro: 3.6 PHP-Version: 7.4.12 mysqli: 5.7.32 Thanks a lot in advence Ernesto