prevent overflowing of splitview views and parts

fixes #78167

src/vs/base/browser/ui/splitview/splitview.css

@@ -30,6 +30,7 @@
 .monaco-split-view2 > .split-view-container > .split-view-view {
 	white-space: initial;
 	position: absolute;
+	overflow: hidden;
 }
 
 .monaco-split-view2 > .split-view-container > .split-view-view:not(.visible) {

src/vs/workbench/browser/media/part.css

@@ -9,6 +9,7 @@
 
 .monaco-workbench .part {
 	box-sizing:	border-box;
+	overflow: hidden;
 }
 
 .monaco-workbench .part > .title {