[Theme: ShopPlus] How to center featured images on slider?

My website it https://www.yeoldefinance.com

I have encountered problems when not using a large enough featured image. If I don’t use a large enough image, the image automatically aligns on the left. I have tried setting margins to auto, but it still hasn’t fixed my problem. How can I have smaller images automatically center themselves?

Here is a snippet of the section of CSS I need help changing.
/* =SLIDER
————————————————————– */

.fp-slider {
margin: 0 0 15px 0;
}

.fp-slides-container {}

.fp-slides, .fp-thumbnail, .fp-prev-next, .fp-nav {
width: 930px;
}

.fp-slides, .fp-thumbnail {
height: 300px;
overflow: hidden;
position: relative;
}

.fp-title {
font-family: ‘Oswald’, sans-serif;
color: #fff;
font-size: 18px;
font-weight: normal;
padding: 0 0 2px 0;
margin: 0;
}

.fp-title a, .fp-title a:hover {
color: #fff;
text-decoration: none;
}

.fp-content {
position: absolute;
bottom: 0;
left: 0;
right: 0;
background: #111;
opacity: 0.7;
filter: alpha(opacity = 70);
padding: 10px 15px;
overflow: hidden;
}