Update app.css for layout and overflow adjustments

src/app/app.css

@@ -25,11 +25,12 @@ html,
 body,
 #root {
   margin: 0;
-  min-height: 100%;
+  height: 100%;
 }
 
 body {
   min-height: 100vh;
+  overflow: hidden;
   background:
     radial-gradient(circle at top, rgba(80, 96, 120, 0.35) 0%, rgba(23, 28, 37, 0) 42%),
     linear-gradient(180deg, #1b2029 0%, #101318 100%);
@@ -63,9 +64,10 @@ button:disabled {
 .app-shell {
   display: grid;
   grid-template-rows: 64px minmax(0, 1fr) 36px;
-  min-height: 100vh;
+  height: 100vh;
   gap: 12px;
   padding: 12px;
+  overflow: hidden;
 }
 
 .toolbar {
@@ -146,6 +148,7 @@ button:disabled {
   grid-template-columns: minmax(240px, 280px) minmax(0, 1fr) minmax(280px, 320px);
   gap: 12px;
   min-height: 0;
+  overflow: hidden;
 }
 
 .runner-workspace {
@@ -153,6 +156,7 @@ button:disabled {
   grid-template-columns: minmax(0, 1fr) minmax(280px, 320px);
   gap: 12px;
   min-height: 0;
+  overflow: hidden;
 }
 
 .side-column {
@@ -160,6 +164,11 @@ button:disabled {
   flex-direction: column;
   gap: 12px;
   min-height: 0;
+  min-width: 0;
+  overflow-y: auto;
+  overflow-x: hidden;
+  overscroll-behavior: contain;
+  scrollbar-gutter: stable;
 }
 
 .panel {