fix: maintain app content width when opening Viewer

- with 'position: fixed' sidebar is ripped out of flex container and main content fills the space before modal is rendered (that is visible to end users)
- this also respects having app navigation open/closed (did not test without navigation though)

Signed-off-by: Maksim Sukharev <antreesy.web@gmail.com>

Author: Antreesy

apps/viewer/apps/viewer/src/views/Viewer.vue

@@ -1427,6 +1427,15 @@ body:has(#viewer) {
 		width: calc(var(--app-sidebar-width) + var(--body-container-margin));
 	}
 
+	.app-navigation ~ #app-content-vue:has(~ #app-sidebar-vue:not([style*="display: none"])) {
+		flex-basis: calc(100% - 300px - clamp(300px, 27vw, 500px));
+	}
+
+	#app-content-vue:first-child:has(~ #app-sidebar-vue:not([style*="display: none"])),
+	.app-navigation--closed ~ #app-content-vue:has(~ #app-sidebar-vue:not([style*="display: none"])) {
+		flex-basis: calc(100% - clamp(300px, 27vw, 500px));
+	}
+
 	#header {
 		visibility: hidden;
 	}