Improves graph column resize handles

Matches graph column handles to vscode styles

src/webviews/apps/plus/graph/graph.scss

@@ -325,3 +325,41 @@ body {
 		background-color: var(--vscode-scrollbarSlider-activeBackground);
 	}
 }
+
+.graph-header {
+	& .resizable-handle.horizontal {
+		--sash-size: 4px;
+		--sash-hover-size: 4px;
+
+		border-right: none !important;
+		width: var(--sash-size) !important;
+		height: 100vh !important;
+		z-index: 1000;
+
+		&:before {
+			content: "";
+			pointer-events: none;
+			position: absolute;
+			width: 100%;
+			height: 100vh;
+			transition: background-color .1s ease-out;
+			background: transparent;
+
+			width: var(--sash-hover-size);
+			left: calc(50% - var(--sash-hover-size)/2);
+		}
+
+		&:hover, &:active {
+			&:before {
+				transition-delay: 0.2s;
+				background-color: var(--vscode-sash-hoverBorder);
+			}
+		}
+	}
+}
+
+.graph-container {
+	& .resizable-handle.horizontal {
+		display: none;
+	}
+}