styles.css

img {
    border-radius: 10px;
}

.stApp {
    background: linear-gradient(to bottom, rgba(247,251,252,1) 0%,rgba(217,237,242,1) 40%,rgba(173,217,228,1) 100%); /* W3C, IE10+, FF16+, Chrome26+, Opera12+, Safari7+ */
}