Plugin’s CSS is breaking my site’s styles

in this file: /wp-content/plugins/tweetshare-click-to-tweet/assets/css/styles.css

The following lines:

a{
    border-bottom: none !important;
    text-decoration: none;
}

Are messing up my site and producing buttons without a bottom border/line. see https://www.dropbox.com/s/yztajjxtviqnlev/Screenshot%202017-01-12%2009.40.14.png?dl=0

Why is it that you apply this to ALL a tags and not to only tags with your classes on them? I noticed that the border-bottom: none !important; is repeated in various lines below it within this file.

It doesn’t make sense to have this without a class attached to it.