Improved timegroup-message element contrast (#834)

* Added `@timegroup-message-color` variable

* Added contrast `@timegroup-message-color`

Author: oleksandr-danylchenko

src/less/Variables.less

@@ -67,6 +67,8 @@
 @minor-ticks-line-color: 		@minor-ticks-color;
 @major-ticks-line-color: 		darken(@minor-ticks-line-color,10);
 
+@timegroup-message-color:       darken(@ui-background-color-darker,2);
+
 @brand-color: 					darken(@ui-background-color,15);
 
 @era-color-1: 					@color-theme-complement;

src/less/themes/contrast/Variables.less

@@ -52,13 +52,13 @@
 ================================================== */
 @ui-background-color:			darken(@color-background, 5);
 @ui-background-color-darker:	darken(@color-background, 10);
+
 @marker-color: 					darken(@ui-background-color,5);
 @marker-outline-color: 			darken(@ui-background-color,40);
 @marker-selected-text-color: 	@color-background;
 @marker-text-color: 			darken(@marker-color,50);
 @marker-dot-color: 				darken(@marker-color, 33);
 @marker-dot-hover-color: 		darken(@marker-dot-color, 33);
-
 @marker-color-menubar-button:	darken(@marker-color,47);
 
 @minor-ticks-color:				darken(@ui-background-color,49);
@@ -67,6 +67,8 @@
 @minor-ticks-line-color: 		@minor-ticks-color;
 @major-ticks-line-color: 		darken(@minor-ticks-line-color,10);
 
+@timegroup-message-color:       darken(@ui-background-color-darker,47);
+
 @brand-color: 					darken(@ui-background-color,49);
 
 @era-color-1: 					@color-theme-complement;

src/less/timenav/TL.TimeGroup.less

@@ -22,8 +22,8 @@
 
 	.tl-timegroup-message {
 		//z-index:6;
-		color:darken(@ui-background-color-darker,2);
-		text-shadow: @color-background 0px 2px 2px;
+		color: @timegroup-message-color;
+		text-shadow: @color-background 0 2px 2px;
 		margin-left:80px;
 		//background-color:@ui-background-color;