Potentially very newbie question here but just wanted to confirm, when overriding CSS in the Themes / Appearance tab in Admin, do I need to identify the entire class or just the part of the class I want to change?

For example I want to change this original class so that the padding is less:

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.ow_box_empty .ow_newsfeed_btns {    background: none repeat scroll 0 0 #fff1db;    border: 1px solid #dadada;    margin-left: -6px;    margin-right: -6px;    padding: 10px;}

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Can I simply enter this or do I need to paste the entire class with only changes to the padding attribute?

.ow_box_empty .ow_newsfeed_btns {
    padding: 5px;}

Thanks,