Change column width of registration form

Hello,

You can add some custom Css, see this tutorial to see how to proceed.
Some custom css, like this must do the trick :
.your_html_class {
width: your required value;
}

In order to get your html element class, point it, and right-click, then select inspect (inspector or inspector tool), to see the html code of your element.
Hope this will help you to get what you need.

Regards