A theme based red and black with a hint of anime (Up to date as of 9/10/2017)

To change the background, just add the code below with a different link in the Custome CSS tab of the BetterDiscord settings:( Also be sure to add the s after http when you change the pic or it won't appear )

.app {
    background-image: url("https://i.imgur.com/P0k3VRY.jpg") !important;
    background-size: 1500px 900px !important;
    background-repeat: no-repeat !important;
}
/* Just change the link to whatever picture, including the `s` in `https` */

.callout-backdrop {
    opacity:0.9 !important;
    background: url("https://i.imgur.com/CcntY8Y.jpg") !important;
    background-size: 1500px 900px !important;
    background-repeat: no-repeat !important;
}

A theme based Re:Zero kara Hajimeru Isekai Seikatsu anime (Up to date as of 9/10/2017)

Code for the background picture:

.app {
    background-image: url("https://i.imgur.com/w7UVsOs.jpg") !important; 
    background-size: cover !important;
}
/* Just change the link to whatever picture of Emelia, Rem, or Ram including the `s` in `https` */

.callout-backdrop {
    opacity:0.9!important;
    background: url("https://i.imgur.com/eeDIMtw.jpg")!important;
    background-size: cover !important;
    background-position: center !important;
}

Thanks for coming~~ ^~^