Child-themes are easy to set up and offer great flexibility, they are pretty much required for any php file edits. Since you are only changing css styles you could also use a custom css plugin if that seems easier.
I am not an expert at all, but I know that if you want to make changes in your theme it’s better you create a child for it, or when you update the theme you will lose all changes.
I use a plugin called Child Themify and it works great.
@simplywell-nest – you’re not choosing child theme, you need to create it. Please read this page to understand better how child themes work. You can use a plugin to create a child theme like @mysweethings suggested. I usually use One Click Child Theme plugin for that.