I am applying this theme to an older application where I cannot add the .form-control class to the inputs themselves. A lot of these inputs are in tables and such so I would just like to use LESS to extend the .form-input class to be the default styles for all inputs unless overridden by specific styles. I seen this idea in another answer but I am unsure how to do it properly. I need to do something like

&:extend(.form-control all);
This is the theme: almsaeedstudio.com/themes/AdminLTE/index2.html

its free and here is the git repo: https://github.com/almasaeed2010/AdminLTE