Userstyle and userscript for grayscale and pinq UI for November 2021.

script.js

// www.youtube.com theme by god.DLL@iCloud.com (cc) 2021
// gist.github.com/godDLL/ab5e8ab3e9b4dc278ebe69341ad3fbde

document.body.onload= function () {
  var i= function i () {
    var v= document.getElementById('search-form')
    if (null == v){
      setTimeout( i, 49)
      return
    }
    v= v.children[0]

    var r= 95,  g= 62,  b= 149
    var SI= 27500,  HM= 111,  ts= +new Date
    var QQ= Math.round( 3* HM   /2.47),  QF= 200

    var s= function s () {
      var ls= +new Date

      if (ls < ts){
        setTimeout( s, SI *.125)
        return
      }

      v.style.backgroundColor= 'rgb('+
        Math.round(r)+','+Math.round(g)+','+Math.round(b)+')'

      ts += SI - (ls - ts) + QF *3999

      var qc= Math.abs( QQ - Math.round( (r+g+b) /2.47))

      if (QF >= qc){
        setTimeout( s, SI *.85)
        QF= qc

      } else {
        v.style.backgroundColor= 'rgb('+HM+','+HM+','+HM+')'
        return
      }

      if (r < HM)
        r += 2.5  / QF
      if (g < HM)
        g += 12.25/ QF
      if (b > HM)
        b -= 9    / QF

    }//>
    s()
  }//>
  i()
}

style.css

/* www.youtube.com theme by god.DLL@iCloud.com (cc) 2021
   gist.github.com/godDLL/ab5e8ab3e9b4dc278ebe69341ad3fbde
*/

#search-form div.ytd-searchbox {
    background-color: #657;
}

svg.style-scope.yt-icon {
    filter: grayscale(1);
}

yt-img-shadow.style-scope.ytd-thumbnail.no-transition {
    filter: grayscale(1);
    opacity: .67;
}

ytd-display-ad-renderer.style-scope.ytd-rich-item-renderer {
    display: none;
}

.ytd-browse.grid #primary {
   background-color: #d0b0c0;
}

ytd-watch-flexy.ytd-page-manager {
   background-color: #e0c0d0;
}

#content.ytd-expander {
    background-color: #debece;
    border-radius: 7px;
    padding-left:.75em;
    position: relative;
    left:-.75em;
    padding-top:.25em;
    padding-bottom:.1em;
    border-left:      #c9a9b9 solid 1px;
    border-top:      #c0a0b0 solid 1px;
    border-right:    #efcfdf solid 1px;
    border-bottom: #eacada solid 1px;
}

#content > .yt-related-chip-cloud-renderer {
    background-color: none !important;
}

#primary-inner #meta {
    margin-left:-1.75em;
    margin-right:1em;
}

#items .ytd-watch-next-secondary-results-renderer {
    background-color:white;
    padding-left: 1em;
    margin-right:-2em;
    margin-left:-2em;
    zoom:.89;
}

#items > .ytd-watch-next-secondary-results-renderer:first-child {
    background-color: #c0a0b0 !important;
    margin-bottom:1em;
    margin-left:-8em;
    margin-right:-3em;
    border-radius: 7px;
}

#items > .ytd-watch-next-secondary-results-renderer:first-child .yt-chip-cloud-renderer {
    background-color: #c0a0b0 !important;
    color: black !important
}

#items > .ytd-watch-next-secondary-results-renderer:first-child .iron-selected {
    border-color: white !important;
    font-weight: bold;
}


.ytd-watch-flexy {
    background-color: #cfafbf !important;
}

div#scroll-container {
    background-color: none !important;
}

ytd-mini-guide-renderer.style-scope.ytd-app {
    background-color: gray;
}

ytd-mini-guide-entry-renderer.style-scope.ytd-mini-guide-renderer {
    background-color: gray;
}

#right-arrow::before {
    background-image: none!important;
}

#left-arrow::after {
    background-image: none!important;
}

#left-arrow-button, #right-arrow-button {
    background-color: gray!important;
}



yt-formatted-string#video-title {
    color: #000!important;
    font-size: 1.5em !important;
}

.byline.style-scope.ytd-rich-grid-media {
    background-color: #a89;
    padding: 8px;
    color:#867!important;
}

a.yt-simple-endpoint.yt-formatted-string,
span.ytd-video-meta-block,
yt-formatted-string,
span#video-title {
    color: #657!important;
}

yt-formatted-string.ytd-video-renderer {
    color:#333 !important;
    font-size: 1.5em !important;
}

yt-formatted-string.ytd-video-primary-info-renderer {
    color:#333 !important;
    font-size: 1.25em !important;
}

span.yt-formatted-string {
   color: #ecd !important;
   font-size: 1em !important;
}

#columns span.yt-formatted-string {
   color: #546 !important;
   font-size: 1em !important;
}

.ytd-video-view-count-renderer,
.more-button, .less-button,
.ytd-comment-action-buttons-renderer {
   color: #876 !important;
}

.ytd-menu-service-item-renderer,
.ytd-playlist-add-to-option-renderer {
   color: #a98 !important;
}

tp-yt-paper-button.ytd-subscribe-button-renderer {
    background:none !important;
}

License CC-BY, free to do whatever. Yours to fuck up.