UI: Style dock widgets in dark and rachni themes

Closes jp9000/obs-studio#1141

UI/data/themes/Dark.qss

@@ -67,6 +67,31 @@ QListWidget::item:selected:!active {
     background-color: rgb(48,47,48);
 }
 
+/* Dock Widget */
+
+QDockWidget::title {
+    text-align: center;
+    background-color: QLinearGradient(x1: 0, y1: 0, x2: 0, y2: 1,
+        stop: 0 rgb(86,85,86),
+        stop: 0.1 rgb(82,81,82),
+        stop: 0.5 rgb(78,77,78),
+        stop: 0.9 rgb(74,73,74),
+        stop: 1 rgb(70,69,70));
+}
+
+QDockWidget::close-button, QDockWidget::float-button {
+    border: 1px solid transparent;
+    background: transparent;
+    padding: 0px;
+}
+
+QDockWidget::close-button:hover, QDockWidget::float-button:hover {
+    background: transparent;
+}
+
+QDockWidget::close-button:pressed, QDockWidget::float-button:pressed {
+    padding: 1px -1px -1px 1px;
+}
 
 /* Group Box */
 

UI/data/themes/Rachni.qss

@@ -105,6 +105,37 @@ QListWidget::item:hover:!active {
 	border: none;
 }
 
+/***********************/
+/* --- Dock widget --- */
+/***********************/
+
+QDockWidget {
+	background: rgb(49, 54, 59); /* Blue-gray */
+	border: 1px solid rgb(58, 64, 69); /* Light Blue-gray */
+}
+
+QDockWidget::title {
+	text-align: left;
+	background: rgb(35, 38, 41); /* Dark Gray */
+	padding-left: 5px;
+}
+
+
+QDockWidget::close-button, QDockWidget::float-button {
+	border: 1px solid transparent;
+	border-radius: 2px;
+	background: transparent;
+}
+
+QDockWidget::close-button:hover, QDockWidget::float-button:hover {
+	background: rgba(255, 148, 194, 0.25); /* Light Pink (Secondary Light) */
+}
+
+QDockWidget::close-button:pressed, QDockWidget::float-button:pressed {
+	padding: 1px -1px -1px 1px;
+	background: rgba(255, 148, 194, 0.25); /* Light Pink (Secondary Light) */
+}
+
 
 /***********************/
 /* --- Group Boxes --- */