My Chrome Dev Tools Skin incorporates the sleek visual style of codepen.io with some of my own usability enhancements. Pictured here with Monokai color scheme ( http://imgur.com/mbrqt ).

Custom.css

/*

Chrome Developer Tools - Monokai Color Theme
Author: Béres Máté Csaba / bjmatt.com / @bjmatt / beres.mate@bjmatt.com
-----------------------------------------------------------------------------------------------------------

Installation:

1. Find your Chrome's user stylesheets directory:

   Mac: ~/Library/Application Support/Google/Chrome/Default/User StyleSheets/
   Windows: C:\Users\**Your Username**\AppData\Local\Google\Chrome\User Data\Default\User StyleSheets\
   Ubuntu (Chromium): ~/.config/chromium/Default/User StyleSheets/

2. Replace the existing "Custom.css" file with this one

3. No restart needed, changes are applied immediately
-----------------------------------------------------------------------------------------------------------

Inspired by:

Monokai color scheme (slightly modified)

Ben Truyman's IR_Black Skin:
https://gist.github.com/1150520

Darcy Clarke:
http://darcyclarke.me/design/skin-your-chrome-inspector
----------------------------------------------------------------------------------------------------------*/


/* GENERIC TYPO, COLORS, SIDEBAR
----------------------------------------------------------------------------------------------------------*/

#-webkit-web-inspector #main-panels .script-view,
#-webkit-web-inspector #main-panels .source-code,
#-webkit-web-inspector #main-panels .text-editor-contents {
	background-color: #272822 !important;
	font-size: 15px !important;
	line-height: 18px !important;
	tab-size: 2 !important;
	font-family: "Bitstream Vera Sans Mono", monospace !important;
}

#-webkit-web-inspector .monospace,
#-webkit-web-inspector .source-code {
	font-size: 13px !important;
	font-family: "Bitstream Vera Sans Mono", monospace !important;
}

#-webkit-web-inspector #main-panels .resource-headers-view .source-code {
	background-color: #fff !important;
	font-size: 13px !important;
	line-height: 14px !important;
}

#-webkit-web-inspector .status-bar {
  background: -webkit-linear-gradient(#505050,#383838) !important;
	border-top: 1px solid #222 !important;
	border-bottom: 1px solid #222 !important;
	border-color: #222 !important;
	box-shadow: inset 0 1px 0 #6E6E6E, 0 2px 2px rgba(0, 0, 0, 0.4), 0 -2px 2px rgba(0, 0, 0, 0.4) !important;
}

#-webkit-web-inspector #main-status-bar {
	height: 24px !important;
	border-bottom-width: 0 !important;
}

#-webkit-web-inspector .long-click-glyph {
	display: none !important;
}

#-webkit-web-inspector .status-bar li,
#-webkit-web-inspector .status-bar span,
#-webkit-web-inspector .status-bar select {
	color: #F8F8F8 !important;
	font-weight: normal !important;
	text-shadow: none !important;
}

#-webkit-web-inspector .status-bar button.status-bar-item {
	border-left-color: #333 !important;
	border-right-color: #333 !important;
}

#-webkit-web-inspector .status-bar .crumbs {
  text-shadow: none !important;
  color: #f8f8f8 !important;
}

#-webkit-web-inspector .status-bar-items {
	border: 0 none !important;
}

#-webkit-web-inspector .status-bar-select-container,
#-webkit-web-inspector .status-bar-select-container select {
	border: 0 none !important;
}

#-webkit-web-inspector .status-bar .crumbs .crumb {
	-webkit-border-image: none !important;
	text-shadow: none !important;
	padding: 0 14px !important;
}

#-webkit-web-inspector .status-bar .crumbs .crumb.selected {
	background-color: rgba(0,0,0,0.4) !important;
}

#-webkit-web-inspector #toolbar {
	background: -webkit-linear-gradient(#505050,#383838) !important;
	border-top: 1px solid #222 !important;
	border-bottom: 1px solid #222 !important;
	box-shadow: inset 0 1px 0 #6E6E6E, 0 2px 2px rgba(0, 0, 0, 0.4), 0 -2px 2px rgba(0, 0, 0, 0.4) !important;
	height: auto !important;
}

#-webkit-web-inspector .toolbar-label {
	color: #999 !important;
	position: relative !important;
	top: 0px !important;
}

#-webkit-web-inspector #toolbar > button {
	box-shadow: none !important;
	border: 0 none !important;
	line-height: 22px !important;
	padding: 4px 14px 6px !important;
	cursor: pointer !important;
}

#-webkit-web-inspector button:hover,
#-webkit-web-inspector .toolbar-item.toggleable.toggled-on {
	background-color: rgba(0,0,0,0.4) !important;
}

button.status-bar-item.toggled-on .glyph {
	background-color: yellow !important;
}

#-webkit-web-inspector #toolbar > button:hover .toolbar-label,
#-webkit-web-inspector .toolbar-item.toggleable.toggled-on .toolbar-label {
	color: #f8f8f8 !important;
}

#-webkit-web-inspector #toolbar div:first-child {
	display: none !important;
}

#-webkit-web-inspector #toolbar > div:first-child {
	display: block !important;
}

#-webkit-web-inspector #main {
	top: 34px !important;
}

.split-view-sidebar-right .pane .sidebar-separator {
	background-image: -webkit-linear-gradient(#505050,#383838) !important;
	padding: 2px 5px !important;
	border-top: 1px solid #636363 !important;
	border-bottom: 1px solid black !important;
	color: #eee !important;
	text-shadow: #222 0 1px 0 !important;
	white-space: nowrap !important;
	text-overflow: ellipsis !important;
	overflow: hidden !important;
	font-size: 11px !important;
}


/* ELEMENTS
----------------------------------------------------------------------------------------------------------*/
#storage-views .webkit-html-comment,
#elements-content .webkit-html-comment,
#network-views .webkit-html-comment,
.resources .script-view .webkit-html-comment,
#storage-views .webkit-css-comment,
#elements-content .webkit-css-comment,
#network-views .webkit-css-comment,
.resources .script-view .webkit-css-comment,
.console-message .webkit-css-comment,
.console-message .webkit-html-comment {
	color: #75715e !important;
}

#storage-views .webkit-html-tag,
#elements-content .webkit-html-tag,
#network-views .webkit-html-tag,
.resources .script-view .webkit-html-tag,
.console-message .webkit-html-tag,
 .console-message .webkit-html-tag-name {
	color: #f92672 !important;
}

#storage-views .webkit-html-attribute-name,
#elements-content .webkit-html-attribute-name,
#network-views .webkit-html-attribute-name,
.resources .script-view .webkit-html-attribute-name,
.console-message .webkit-html-attribute-name {
	color: #a6e22e !important;
}

#storage-views .webkit-html-attribute-value,
#elements-content .webkit-html-attribute-value,
#network-views .webkit-html-attribute-value,
.resources .script-view .webkit-html-attribute-value,
.console-message .webkit-html-attribute-value {
	color: #e6db74 !important;
}

#storage-views .webkit-html-text-node,
#elements-content .webkit-html-text-node,
#network-views .webkit-html-text-node,
.resources .script-view .webkit-html-text-node,
#storage-views .webkit-html-css-node,
#elements-content .webkit-html-css-node,
#network-views .webkit-html-css-node,
.resources .script-view .webkit-html-css-node,
.console-message .webkit-html-text-node {
	color: #c1c1c1 !important;
}

#storage-views .webkit-html-js-node,
#elements-content .webkit-html-js-node,
#network-views .webkit-html-js-node,
.resources .script-view .webkit-html-js-node {
	color: #c2c3c3 !important;
}

#storage-views .webkit-html-resource-link,
#elements-content .webkit-html-resource-link,
#network-views .webkit-html-resource-link,
.resources .script-view .webkit-html-resource-link,
#storage-views .webkit-html-external-link,
#elements-content .webkit-html-external-link,
#network-views .webkit-html-external-link,
.resources .script-view .webkit-html-external-link,
.console-message .webkit-html-external-link {
	color: #a6e22e !important;
}

#storage-views .webkit-css-selector,
#elements-content .webkit-css-selector,
#network-views .webkit-css-selector,
.resources .script-view .webkit-css-selector {
	color: #a6e22e !important;
}

#storage-views .webkit-css-property,
#elements-content .webkit-css-property,
#network-views .webkit-css-property,
.resources .script-view .webkit-css-property,
#storage-views .webkit-css-at-rule,
#elements-content .webkit-css-at-rule,
#network-views .webkit-css-at-rule,
.resources .script-view .webkit-css-at-rule {
	color: #66d9ef !important;
}

#storage-views .webkit-css-number,
#elements-content .webkit-css-number,
#network-views .webkit-css-number,
.resources .script-view .webkit-css-number,

#storage-views .webkit-css-url,
#elements-content .webkit-css-url,
#network-views .webkit-css-url,
.resources .script-view .webkit-css-url,

#storage-views .webkit-css-color,
#elements-content .webkit-css-color,
#network-views .webkit-css-color,
.resources .script-view .webkit-css-color,

#storage-views .webkit-css-string,
#elements-content .webkit-css-string,
#network-views .webkit-css-string,
.resources .script-view .webkit-css-string,

#storage-views .webkit-css-keyword,
#elements-content .webkit-css-keyword,
#network-views .webkit-css-keyword,
.resources .script-view .webkit-css-keyword {
	color: #f92672 !important;
}

#elements-content .highlight {
	color: #f1f1f1;
}

#elements-content li.hovered:not(.selected) .selection {
	background: rgba(255, 255, 255, .2) !important;
}

#elements-content .selection.selected {

}

#elements-content ol:focus li.selected .selection {
	background: #3f4360 !important;
}

#elements-content .selected .highlight {

}

#elements-content .selected {
	background-color: rgba(255, 255, 255, 0.07) !important;
	border-left: 5px solid #f8f8f8;
	border-right: 10px solid yellow;
	padding-top: 10px !important;
	padding-bottom: 10px !important;
	padding-right: 10px !important;
	left: -5px !important;
	position: relative;
}

#elements-content .editing {
	background-color: #242424 !important;
	color: #c1c1c1 !important;
}

#elements-content .parent::before {
	content: url(chrome-devtools://devtools/Images/treeRightTriangleWhite.png) !important;
	position: relative;
	z-index: 999;
}

#elements-content .parent.expanded::before {
	content: url(chrome-devtools://devtools/Images/treeDownTriangleWhite.png) !important;
}

.styles-element-state-pane > table td {
	color: #aaa;
}

/* SCRIPTS
----------------------------------------------------------------------------------------------------------*/
#-webkit-web-inspector #main-panels .webkit-line-content {
	padding-left: 4px;
}

#-webkit-web-inspector #main-panels .text-editor-contents,
#-webkit-web-inspector #main-panels .text-editor-contents,
#-webkit-web-inspector #main-panels .text-editor-contents,
#-webkit-web-inspector #main-panels .text-editor-contents,
#-webkit-web-inspector #main-panels .webkit-css-selector {
	color: #c1c1c1 !important;
}

#-webkit-web-inspector #main-panels .text-editor-lines {
	background-color: #272822 !important;
	border-right: none !important;
}

#-webkit-web-inspector #main-panels .text-editor-contents {
	color: #c1c1c1 !important;
}

#-webkit-web-inspector #main-panels .webkit-javascript-keyword {
	color: #66d9ef !important;
}

#-webkit-web-inspector #main-panels .webkit-javascript-string,
#-webkit-web-inspector #main-panels .webkit-javascript-regexp {
	color: #e6db74 !important;
}

#-webkit-web-inspector #main-panels .webkit-javascript-number {
	color: #ae81ff !important;
}

#-webkit-web-inspector #main-panels .webkit-javascript-ident {
	color: #c1c1c1 !important;
}

#-webkit-web-inspector #main-panels .webkit-javascript-comment {
	color: #75715E !important;
}

#-webkit-web-inspector .webkit-execution-line.webkit-line-content {
	background-color: #3d3d3d !important;
	outline: 1px solid #535353 !important;
}

/* CONSOLE
----------------------------------------------------------------------------------------------------------*/
#console-prompt {
	color: #c1c1c1 !important;
	font-size: 13px !important;
}

#console-messages .monospace,
#console-messages .source-code {
	font-size: 13px !important;
}

#console-message {
	font-size: 13px !important;
}

#console-prompt::before {
	background-image: url(data:image/png;base64,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) !important;
	color: #c1c1c1 !important;
}

#console-messages {
	background: #272822;
}

#console-messages a {
  color: #666 !important;
}

#console-messages a:hover {
	color: #999 !important;
}

#console-messages .console-message {
	color: #f1f1f1 !important;
}

#console-messages .console-message, .console-user-command {
	border-bottom: 1px solid #333 !important;
}

#console-messages .console-user-command > .console-message-text {
	color: #ffd2a7 !important;
}

#console-messages .console-formatted-number {
	color: #ff73fd !important;
}

#console-messages .console-formatted-string {
	color: #a8ff60 !important;
}

#console-messages .console-formatted-object {
	color: #bbb !important;
}

#console-messages .console-formatted-undefined {
	color: #666 !important;
}

#console-messages .console-formatted-function {
	color: #bbb !important;
}

#console-messages .console-formatted-regexp {
	color: #e9c062 !important;
}

#console-messages .console-formatted-array {
	color: #a8ff60 !important;
}

.console-message-text {
}

.console-message-text.source-code {
	color: #c1c1c1 !important;
}

#console-messages .console-formatted-object,
#console-messages .console-formatted-function,
#console-messages .console-formatted-null,
#console-messages .console-formatted-node {
	color: #a8ff60 !important;
}

#console-messages .console-group-messages .section .header .title {
	color: #f1f1f1 !important;
}

#console-messages .section .properties .name, .event-properties .name {
	color: #96cbfe !important;
}

#console-messages .console-group-messages .section .header::before,
#console-messages .properties-tree li.parent::before {
	content: url(chrome-devtools://devtools/Images/treeRightTriangleWhite.png) !important;
}

#console-messages .console-group-messages .section.expanded .header::before,
#console-messages .properties-tree li.parent.expanded::before {
	content: url(chrome-devtools://devtools/Images/treeDownTriangleWhite.png) !important;
}

.console-message .outline-disclosure li.parent::before {
	content: url(chrome-devtools://devtools/Images/treeRightTriangleWhite.png) !important;
}

.console-message .outline-disclosure li.parent.expanded::before {
	content: url(chrome-devtools://devtools/Images/treeDownTriangleWhite.png) !important;
}

@-webkit-keyframes webkit-error-level {
	0%   { color: #f77; !important }
	50%  { color: #f00; !important }
	100% { color: #f77; !important }
}

#console-messages .console-error-level .console-message-text {
	color: #f66 !important;
	-webkit-animation-name: webkit-error-level;
	-webkit-animation-duration: 2s;
	-webkit-animation-iteration-count: infinite;
	-webkit-timing-function: ease-in-out;
}

#console-messages .console-user-command::before {
	background-image: url(data:image/png;base64,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) !important;
}

/* SOURCES - CSS
----------------------------------------------------------------------------------------------------------*/
#scripts-split-view .webkit-css-property {
	color: #a6e22e !important;
}

#scripts-split-view .webkit-css-number,
#scripts-split-view .webkit-css-keyword,
#scripts-split-view .webkit-css-color {
	color: #dd2277 !important;
}

#scripts-split-view .webkit-css-comment {
	color: grey !important;
}

.styles-element-state-pane {
	margin-top: -44px !important;
}

.styles-element-state-pane.expanded {
	margin-top: 0 !important;
}

Thanks @craigkeeling!