.post-news .post-thumbnail {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 300px;
    padding: 5px;
    border: 1px solid #eee;
    background: rgba(255, 255, 255, 0.35);
}

.post-news .post-thumbnail img{
    height: auto;
    max-width: 100%;
    width: auto;
    max-height: 310px;
    margin-left: auto;
    margin-right: auto;
}