DevTools: popover, selection and other minor theme tweaks.

third_party/WebKit/Source/devtools/front_end/popover.css

 .popover-container {
     pointer-events: none;
     overflow: hidden;
 }
 
 .popover {
     position: absolute;
     z-index: 600;
     pointer-events: none;
     display: flex;
@@ skipping 19 matching lines @@
 .popover .arrow {
     position: absolute;
     background-image: url(Images/popoverArrows.png);
     width: 19px;
     height: 19px;
     margin-top: -19px;
     top: 0;
     left: 0;
 }
 
+.-theme-with-dark-background .popover .arrow {
+    -webkit-filter: invert(80%);
+}
+
 .popover.top-left-arrow .arrow {
     /* The default is top-left, no styles needed. */
 }
 
 .popover.top-right-arrow .arrow {
     right: 19px;
     left: auto;
 }
 
 .popover.bottom-left-arrow .arrow {
@@ skipping 25 matching lines @@
 .source-frame-popover-tree {
     border-top: 1px solid rgb(184, 184, 184);
     overflow: auto;
     position: relative;
     top: 5px;
     bottom: 0;
     left: 0;
     right: 0;
     margin-top: 1px;
 }