How to exclude certain code from style.css? [closed]

I would not suggest creating a child theme to override a single CSS line. You can simply use the theme customizer and add your CSS to the additional CSS box. Most CSS properties accept an unset or inherit value. So, you can paste the following code into the additional CSS box:

@media (max-width: 991px) and (min-width: 544px){
  .footer-bottom-widgets .columns {
      width: unset;
  }
}

Since the additional CSS is added as inline, the priority is higher than the original CSS, which will override the original styles.