Now I know how to do it, here is the code in case someone wants to try it.
Inside the route
Osclass\oc-content\themes\veronika\css\style.css on line 105, you can find the following style:
.input-box-check label:hover {text-decoration:underline;}
This means that when you pass the mouse over the label of the checkbox it is highlighted like this:
[ ✔] Show email on listing pageSo, if you want to try to see how it is without the underline just change the 'underline' to 'none! Important', as follows:
.input-box-check label:hover {text-decoration:none !important;}
And this is everything. Now your checkbox will always look like this (Unless you change it again, of course):
[ ✔] Show email on listing page
That's it, I say goodbye and I hope it's useful for someone. Greetings.