did some styling changes

packages/grafana-ui/src/components/Tooltip/_Tooltip.scss

@@ -18,9 +18,9 @@ $popper-margin-from-ref: 5px;
 
 .popper__background {
   background: $tooltipBackground;
-  border-radius: $border-radius;
+  border-radius: $border-radius-sm;
   box-shadow: 0 0 2px rgba(0, 0, 0, 0.5);
-  padding: 3px 8px;
+  padding: 4px 8px;
   color: $tooltipColor;
   font-weight: 500;
 
@@ -29,10 +29,10 @@ $popper-margin-from-ref: 5px;
     @include popper-theme($tooltipBackgroundError, $tooltipBackgroundError);
   }
 
-  &.popper__background--brand {
+  /*&.popper__background--brand {
     @include popper-theme($tooltipBackgroundBrand, $tooltipBackgroundBrand);
     @include gradient-vertical($tooltipBackground, $tooltipBackground);
-  }
+  }*/
 }
 
 .popper__arrow {

public/sass/_variables.dark.scss

@@ -307,8 +307,8 @@ $tooltipArrowWidth: 5px;
 $tooltipLinkColor: $link-color;
 $graph-tooltip-bg: $dark-1;
 
-$tooltipBackground: $dark-1;
-$tooltipColor: white;
+$tooltipBackground: $gray-1;
+$tooltipColor: $gray-6;
 $tooltipArrowColor: $tooltipBackground;
 $tooltipBackgroundError: $brand-danger;
 $tooltipBackgroundBrand: $brand-primary;

public/sass/_variables.light.scss

@@ -311,7 +311,6 @@ $tooltipArrowWidth: 5px;
 $tooltipLinkColor: lighten($popover-help-color, 5%);
 $graph-tooltip-bg: $gray-5;
 
-$tooltipBackground: $popover-help-bg;
 $tooltipBackground: $gray-1;
 $tooltipColor: $gray-7;
 $tooltipArrowColor: $tooltipBackground; // Used by Angular tooltip