rainbow border

<style>
#rainbow {
border: 3px solid;
border-image-slice: 1;
border-image-source: linear-gradient(to bottom right, #b827fc 0%, #2c90fc 25%, #b8fd33 50%, #fec837 75%, #fd1892 100%);
color:#fff;
}
</style>

<div id="rainbow"><img src=https://www.rover.com/blog/wp-content/uploads/2019/06/cat-4223305_1920-300x200.jpg></div>