Firefox CSS (https://github.com/evanswa0606/firefox-simpletheme with adjustments)

userChrome.css

:root {
	--uc-bg-color: #2e3440;
	--uc-show-new-tab-button: none;
	--uc-show-tab-separators: none;
	--uc-tab-separators-color: none;
	--uc-tab-separators-width: none;
	--uc-tab-fg-color: #d8dee9;
}
/* Options with pixel amounts could need to be adjusted, as this only works for my laptop's display */
#titlebar {
	-moz-box-ordinal-group: 2 !important;
}
#nav-bar {
	margin-left: 3vw !important;
}
#nav-bar-customization-target {
	margin-left: 25px !important;
}
.titlebar-buttonbox-container {
	background-color: rgb(50,50,52);
	margin-top: -60px !important;
}
#TabsToolbar {
	min-height: 28px !important;
}
.tabbrowser-tab:not([pinned]){
	max-width: 100vw !important;
}
.tabbrowser-tab:not([fadein]),
#page-action-buttons,
.titlebar-spacer,
.tab-line,
#tracking-protection-icon-container,
#identity-box {
	display: none !important;
	border: none !important;
}
#urlbar-background, .titlebar-buttonbox-container, #nav-bar, .tabbrowser-tab:not([selected]) .tab-background{
    background: var(--uc-bg-color) !important;
	border: none !important;
}
#urlbar[breakout][breakout-extend] {
    top: calc((var(--urlbar-toolbar-height) - var(--urlbar-height)) / 2) !important;
    left: 0 !important;
    width: 100% !important;
}

#urlbar[breakout][breakout-extend] > #urlbar-input-container {
    height: var(--urlbar-height) !important;
    padding-block: 0 !important;
    padding-inline: 0 !important;
}

#urlbar[breakout][breakout-extend] > #urlbar-background {
    animation-name: none !important;
    box-shadow: none !important;
}
#urlbar-background {
	box-shadow: none !important;
}
#tabs-newtab-button {
	display: var(--uc-show-new-tab-button) !important;
}
.tabbrowser-tab::after {
	border-left: var(--uc-tab-separators-width) solid var(--uc-tab-separators-color) !important;
	display: var(--uc-show-tab-separators) !important;
}
.tabbrowser-tab[first-visible-tab][last-visible-tab]{
	background-color: var(--uc-bar-bg-color) !important;
}
.tab-close-button.close-icon {
	display: none !important;
}
.tabbrowser-tab:hover .tab-close-button.close-icon {
	display: block !important;
}
#urlbar-input {
	text-align: center !important;
}
#urlbar-input:focus {
	text-align: left !important;
}
#urlbar-container {
	margin-left: 3vw !important;
}
.tab-text.tab-label {
	color: var(--uc-tab-fg-color) !important;
}
#navigator-toolbox {
	border-bottom: 0px solid red !important;
	background: var(--uc-bg-color) !important;
}