https://twitter.com/LIA_CLEF さんの力添えのお陰です。

DiscordStreamKitVoice4KModern.css

/* 4K環境に合わせる */
body {
    overflow: hidden;
    white-space: nowrap;
    transform-origin: top left;
    transform: scale(1.5); /* サイズ調整は、OBS側で拡大縮小せずここで調整する */
}

/* ソーシャルディスタンス */
li {
    margin-bottom: 1em !important;
}

/* アバター画像のborderが緑に光るインジケータを、名前も含めたカード型にする */
img {
    object-fit: contain;
    object-position: 0%;
    width: 300px !important;
    border: none;
    border: 4px solid transparent !important;
    border-radius: 16px !important;
    float: left;
    box-shadow: 0px 0px 16px -6px black;
}
/* 無言時の背景色 */
img:not(img[class*="peaking"]) {
    border-color: rgba(32,34,37,0.2) !important;
    background-color: rgba(32,34,37,0.6);
}
/* 発言時の背景色 */
img[class*="peaking"] {
    border-color: var(--status-green) !important;
    background-color: rgba(87,201,149);
}

/* 名前 */
li > div {
    position: absolute;
    left: 0;
    margin-left: 70px;
}
span {
    background-color: transparent !important;
    font-size: 22px !important;
    line-height: 26px !important;
    display: block;
    max-width: 240px;
    text-overflow: ellipsis;
    overflow: hidden;
}

.voice-container .voice-states .voice-state .avatar:not(.speaking) {
    border-color: rgba(32,34,37,0.2) !important;
    background-color: rgba(32,34,37,0.6);
}
.voice-container .voice-states .voice-state .speaking {
    background-color: rgba(87,201,149,0.9);
}
.voice-container .voice-states .voice-state .user {
    position: absolute;
    padding: .5em !important;
    padding-top: 0;
    padding-left: 0;
}
.voice-container .voice-states .voice-state .user .name {
    background-color: transparent !important;
    font-family: "Noto Sans JP" !important;
    font-weight: 1;
    font-size: 1em !important;
    line-height: 1em !important;
    color: #fff !important;
}
    font-weight: 1;
    font-size: 36px !important;
    line-height: 36px !important;
    color: #fff !important;
}