Is this done in the Stylesheet (style.css), which can be edited in WordPress > Appearance > Editor or in the Cpanel. Below is the code. But I do not see any changes from the ones I made in the jetpack-carousel.css.
/*////////////////////////////////////////////////////////////////////
// 07 - Buttons
////////////////////////////////////////////////////////////////////*/
.jp-carousel-close-hint { font-size: 30px !important; }
a.button, #footer a.button, #searchsubmit, input[type="submit"] {
font-size: 12px;
background: #757575 url(images/btn_bkg.png) repeat-x;
display: inline-block;
color: #fff;
text-decoration: none;
-moz-box-shadow: 0 1px 3px rgba(0,0,0,0.3);
-webkit-box-shadow: 0 1px 3px rgba(0,0,0,0.3);
box-shadow: 0 1px 3px rgba(0,0,0,0.3);
text-shadow: 0 -1px 1px rgba(0,0,0,0.3);
position: relative;
cursor: pointer;
font-weight: bold;
padding: 5px 15px 5px;
border: 1px solid rgba(0,0,0,.2);
-webkit-border-radius: 5px;
-moz-border-radius: 5px;
border-radius: 5px;
margin: 0 5px 0 0;
line-height: normal !important;
}
a.button, #footer a.button {
padding: 6px 15px 5px;
}
#searchsubmit {
padding: 5px 15px 6px;
}
.button:hover, #footer a.button:hover, #searchsubmit:hover, input[type="submit"]:hover {
background-color: #595959;
color: #fff;
}