Overwrite CSS with without deleting it

I have some css in the theme that I am using, I want to keep the stock style.css without deleting any of it. I want to use my child-theme style.css to remove or hide some values of a class. I would like to do this so I do not have to update my css with each new theme update.

This is what is in the stock theme

.et_pt_portfolio_entry {
border: 1px solid #dadada;
border-bottom: 1px solid #b7b7b7;
background: #fff; 
padding: 5px;
-moz-box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.1);
-webkit-box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.1);
box-shadow: 0px 1px 2px rgba(0, 0, 0, 0.1);
margin-bottom: 7px;
}

This is what I want to use in its place

    .et_pt_portfolio_entry {
    margin-bottom: 7px;
    padding: 5px;
    }

Normally I use display:none but I want to keep that class displaying, I just want to remove the other values without deleting the stock file.

Thoughts?

Assuming you have your child theme set up correctly, placing the following CSS in it which simply resets some of the preset values should get you all the way there.

.et_pt_portfolio_entry {
    border: none;
    border-bottom: none;
    background: transparent; 
    -moz-box-shadow: none;
    -webkit-box-shadow: none;
    box-shadow: none;
    padding: 5px;
    margin-bottom: 7px;
}