Simplify layout and remove unused styles

Removed styles for `.sidebar` and `.top-row` elements, including their background, layout, and responsive behavior, as they are no longer used. Simplified `main` and `article` elements by standardizing `margin` and `padding` to `0`.

Removed media query styles for `.top-row` and `.sidebar` to streamline responsive design. Updated global styles in `app.css` to ensure consistent spacing and alignment for `html`, `body`, `main`, and `.page`.

Focused on creating a cleaner, more minimal design by removing redundant styles and ensuring uniformity across the layout.

EnvelopeGenerator.ReceiverUI/Shared/MainLayout.razor.css

@@ -7,75 +7,11 @@
 
 main {
     flex: 1;
+    margin: 0;
+    padding: 0;
 }
 
-.sidebar {
-    background-image: linear-gradient(180deg, rgb(5, 39, 103) 0%, #3a0647 70%);
-}
-
-.top-row {
-    background-color: #f7f7f7;
-    border-bottom: 1px solid #d6d5d5;
-    justify-content: flex-end;
-    height: 3.5rem;
-    display: flex;
-    align-items: center;
-}
-
-    .top-row ::deep a, .top-row ::deep .btn-link {
-        white-space: nowrap;
-        margin-left: 1.5rem;
-        text-decoration: none;
-    }
-
-    .top-row ::deep a:hover, .top-row ::deep .btn-link:hover {
-        text-decoration: underline;
-    }
-
-    .top-row ::deep a:first-child {
-        overflow: hidden;
-        text-overflow: ellipsis;
-    }
-
-@media (max-width: 640.98px) {
-    .top-row:not(.auth) {
-        display: none;
-    }
-
-    .top-row.auth {
-        justify-content: space-between;
-    }
-
-    .top-row ::deep a, .top-row ::deep .btn-link {
-        margin-left: 0;
-    }
-}
-
-@media (min-width: 641px) {
-    .page {
-        flex-direction: row;
-    }
-
-    .sidebar {
-        width: 300px;
-        height: 100vh;
-        position: sticky;
-        top: 0;
-    }
-
-    .top-row {
-        position: sticky;
-        top: 0;
-        z-index: 1;
-    }
-
-    .top-row.auth ::deep a:first-child {
-        flex: 1;
-        text-align: right;
-        width: 0;
-    }
-
-    .top-row, article {
-        padding: 2rem !important;
-    }
+article {
+    padding: 0 !important;
+    margin: 0 !important;
 }