.thumbnail {
    display: inline-block;
    padding: 4px;
    margin-bottom: 20px;
    line-height: 1.42857143;
    background-color: #fff;
    border: 1px solid #ddd;
    border-radius: 4px;
    -webkit-transition: border .2s ease-in-out;
    -o-transition: border .2s ease-in-out;
    transition: border .2s ease-in-out;
}

.thumbnail:hover, .thumbnail:active, .thumbnail:focus {
  border: 1px solid #F03838 !important;
  padding: 4px !important;
}

.thumbnail>img {
    display: block;
    max-width: 100%;
    height: auto;
}

.thumbnail a>img, .thumbnail>img {
    margin-bottom: auto;
    margin-top: auto;
    margin-right: auto;
    margin-left: auto;
}

.thumbnail {
    display: inline-block;
    padding: 4px;
    margin-bottom: 20px;
    line-height: 1.42857143;
    background-color: #fff;
    border: 1px solid #ddd;
    border-radius: 4px;
    -webkit-transition: border .2s ease-in-out;
    -o-transition: border .2s ease-in-out;
    transition: border .2s ease-in-out;
}

.thumbnail:hover, .thumbnail:active, .thumbnail:focus {
  border: 1px solid #F03838 !important;
  padding: 4px !important;
}

.thumbnail>img {
    display: block;
    max-width: 100%;
    height: auto;
}

.thumbnail a>img, .thumbnail>img {
    margin-bottom: auto;
    margin-top: auto;
    margin-right: auto;
    margin-left: auto;
}

img.post-featured-image {
  width: 100%;
}

Make feature images span 100% of the page
Make feature images span 100% of the page

