@danielbora123 ‘s suggestion is prefectly valid. Kudos to you for finding that rogue style rule – It’s quite hidden.
However, I don’t recommend editing directly the stylesheet, otherwise your changes will be overwritten whenever the theme is updated. A custom CSS editor (Additional CSS) is found at Dashboard – Appereance – Customize – Additional CSS in the Customizer. Also, this code is loaded later, so it should override previous CSS.
So, try adding this in Dashboard – Appereance – Customize – Additional CSS
@media screen and (max-width: 720px){
.search-box {
margin:0;
}
}
You can learn how to use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.
Hope this helps,
Kind regards!