>>/5819/
there's also some dollchan settings that configure it, mainly "reply form display in thread" -> "at bottom"
and the mascots userscript
otherwise it's this

/* Post styling */
.innerPost, .markedPost {
    border-radius: 2px;
    background-color: #2F343ED0;
    padding-right: 12px;
    max-width: 84%;
}
.innerOP {
    border-radius: 2px;
    background-color: #2F343ED0;
    padding-left: 4px;
    padding-right: 4px;
    padding-top: 8px;
    padding-bottom: 8px;
} 
a,
blockquote a {
    color: #A5BCD0;
}
a:hover, 
blockquote a:hover {
    color: #D2DFEA;
}
/* Post (reply) previews */
.de-pview {
    border-radius: 2px;
    background-color: #1D1D21EE;
}
/* > */
.greenText {
    color: #9FBE75;
}

/* Background */
body { 
  background: url(https://i.imgur.com/BiOlhRw.jpeg) no-repeat center center fixed !important; 
  -webkit-background-size: cover;
  -moz-background-size: cover;
  -o-background-size: cover;
  background-size: cover;
}

/* Anchor reply form to top right */
form.form-post {
    position: fixed;
    top: 20px;
    right: 16px;
    background: #2F343ED0;
    padding: 8px !important;
    border-radius: 2px
}

/* Align file attachments to the right */
div#de-file-area {
    text-align: right;
}

/* Larger min size of reply box*/
textarea#fieldMessage {
    min-width: 465px !important;
    min-height: 150px !important;
}

/* Smaller canvas size inputs */
input#oekakiWidth {
    width: 80px;
}
input#oekakiHeight {
    width: 80px;
}
/* actually, just hide it */
td:has(input#oekakiWidth) {
    display: none;
}

/* Hide padding on top of reply form */
div.hField {
    display: none;
}

/* Hide manage board, moderate thread links (may not work on older? FF) */
p:has(a#linkManagement) {
    display: none;
}

/* Hide nav links under reply form */
p.topNav {
    display: none;
}

/* Hide close reply form button */
div.de-parea > div:first-of-type {
    display: none;
}

/* Bottom nav - align to right and hide reply button */
.bottomNav {
    text-align: right;
    border-style: none !important;
    background-color: transparent !important;
    font-size: 100% !important;
    float: none !important;
}
#divPages {
    background-color: #2F343ED0 !important;
    border-radius: 2px !important;
}
a.replyLink {
    display: none;
}


/* Content action form (delete/report) */
/* anchor to bottom right of screen, hide content by default, show on hover */
div.contentAction {
    position: fixed;
    bottom: 16px;
    right: 8px;
    min-width: 64px;
    min-height: 8px;
    padding: 8px !important;
    border-radius: 2px;
    background: #2F343ED0;
}
div.contentAction > * {
    display: none !important;
}
div.contentAction:hover > * {
    display: block !important;
}

/* Remove del link */
a.delLink {
    display: none;
}
label#hideDelLbl {
    display: none !important;
}

/* Hide posting mode banner */
div#modeBanner {
    display: none;
}

/* Site announcements in header */
details > iframe {
    background-color: #676E7CD0;
    border-radius: 4px;
}

/* Dollchan settings panel missing bg */
div.de-win-body {
    background-color: #2F343ED0 !important;
}

.imgLink > img, img[src*="/.media/"], .de-img-embed, .de-video-obj {
    opacity: 1.0 !important;
}