High contrast support for Animation Panel

This patch provides forced-colors overrides to make non-canvas
elements visible in high contrast mode.

Before: https://imgur.com/a/3NmoATe
After: https://imgur.com/a/0MY4S1u
Bug: 1048378
Change-Id: Id2e4a982ef92afff5d5945d39ff543d70c3e2411
Reviewed-on: https://chromium-review.googlesource.com/c/devtools/devtools-frontend/+/2106881
Reviewed-by: Mathias Bynens <mathias@chromium.org>
Commit-Queue: Kalon Hinds <kahinds@microsoft.com>

front_end/animation/animationTimeline.css

@@ -303,6 +303,7 @@ text.animation-timeline-grid-label {
     height: 40px;
     margin: 4px 2px;
     background-color: var(--toolbar-bg-color);
+    border: 1px solid transparent;
     border-radius: 2px;
     flex: 1 1;
     padding: 4px;
@@ -459,4 +460,11 @@ text.animation-timeline-grid-label {
         color: HighlightText;
         background-color: Highlight;
     }
+    .animation-node-description[data-keyboard-focus="true"]:focus {
+        background-color: Canvas;
+        forced-color-adjust: none;
+    }
+    .monospace {
+        forced-color-adjust: auto;
+    }
 }

front_end/ui/popover.css

@@ -7,6 +7,7 @@
 .widget {
     display: flex;
     background: white;
+    border: 1px solid transparent;
     box-shadow: var(--drop-shadow);
     border-radius: 2px;
     overflow: auto;