app.element.io##body:style(font-weight: 500 !important; color: #ffffff !important; text-transform: uppercase !important)
app.element.io##body blockquote:style(font-weight: 500 !important; color: #ffffff !important; text-transform: uppercase !important)
app.element.io##.mx_EventTile:style(font-weight: 500 !important; color: #ffffff !important; text-transform: uppercase !important)
app.element.io##.mx_EventTile_body:style(font-weight: 500 !important; color: #ffffff !important; text-transform: uppercase !important)
app.element.io##.mx_RedactedBody:style(font-weight: 500 !important; color: #ffffff !important)
app.element.io##.mx_DisambiguatedProfile_displayName:style(font-weight: 500 !important; color: #ffffff !important)
app.element.io##.mx_ReplyChain_show:style(font-weight: 500 !important; color: #ffffff !important)
app.element.io##.mx_Pill_text:style(font-weight: 500 !important; color: #000000 !important)
app.element.io##.mx_RoomView_MessageList:style(background-color: #000000 !important)

also install the font fira_code and change to him in the settings and enable irc message layout

download ublock origin for:
iceweasel-uxp: https://wiki.hyperbola.info/doku.php?id=en:system:userspace:application:uxp:iceweasel-uxp_addons
furryfox: https://addons.mozilla.org/addon/ublock-origin/
edge: https://microsoftedge.microsoft.com/addons/detail/ublock-origin/odfafepnkmbhccpbejgmiehpchacaeak