refactor: Update branding and layout in Streamlit app

- Changed the brand subtitle to reflect AI-assisted CT review capabilities.
- Removed the app header section and added a spacer for improved layout above the CT scan/Analysis row.
- Introduced new CSS styles for additional spacing and layout adjustments.

src/static/app.css

@@ -14,6 +14,30 @@ html, body, [class*="css"] {
     max-width: 1100px;
 }
 
+/* Extra breathing room above the first main row (CT scan / Analysis cards) */
+section[data-testid="stMain"] .block-container {
+    padding-top: 3.5rem;
+}
+
+/* Spacer block before the two-column layout — survives Streamlit inner margins */
+section[data-testid="stMain"] [data-testid="stMarkdownContainer"]:has(.main-cards-top-gap) {
+    margin-top: 0 !important;
+    margin-bottom: 0 !important;
+    padding-top: 0 !important;
+    padding-bottom: 0 !important;
+}
+
+section[data-testid="stMain"] [data-testid="stMarkdownContainer"]:has(.main-cards-top-gap) > div {
+    padding: 0 !important;
+    margin: 0 !important;
+}
+
+.main-cards-top-gap {
+    display: block;
+    height: 2.25rem;
+    width: 100%;
+}
+
 section[data-testid="stSidebar"] {
     background-color: #ffffff;
     border-right: 1px solid #e2e8f0;
@@ -53,6 +77,7 @@ section[data-testid="stSidebar"] .block-container {
 
 .brand-sub {
     font-size: 0.75rem;
+    line-height: 1.45;
     color: #64748b;
     margin-top: 2px;
 }
@@ -117,29 +142,6 @@ section[data-testid="stSidebar"] .block-container {
     font-variant-numeric: tabular-nums;
 }
 
-.app-header {
-    background: linear-gradient(120deg, #0f2b46 0%, #164e73 55%, #1a5f8a 100%);
-    border-radius: 12px;
-    padding: 1.75rem 2rem;
-    margin-bottom: 1.5rem;
-    color: #ffffff;
-}
-
-.app-header h1 {
-    margin: 0;
-    font-size: 1.65rem;
-    font-weight: 700;
-    color: #ffffff !important;
-    letter-spacing: -0.02em;
-}
-
-.app-header p {
-    margin: 0.4rem 0 0;
-    color: #cbd5e1;
-    font-size: 0.95rem;
-    font-weight: 400;
-}
-
 .verdict-box {
     border-radius: 10px;
     padding: 1.25rem 1.5rem;

src/streamlit_app.py

@@ -155,7 +155,7 @@ with st.sidebar:
             <div class="brand-mark">SC</div>
             <div>
                 <div class="brand-title">Stroke Classification</div>
-                <div class="brand-sub">Clinical decision support</div>
+                <div class="brand-sub">AI-assisted CT review powered by knowledge-distilled EfficientNet-B0</div>
             </div>
         </div>
         """,
@@ -180,14 +180,9 @@ with st.sidebar:
         unsafe_allow_html=True,
     )
 
-# --- Header (render immediately so the page is not blank) ---
+# Visible gap above the CT scan / Analysis row (Streamlit main chrome eats plain padding)
 st.markdown(
-    """
-    <div class="app-header">
-        <h1>Stroke Detection</h1>
-        <p>AI-assisted CT review powered by knowledge-distilled EfficientNet-B0</p>
-    </div>
-    """,
+    '<div class="main-cards-top-gap" aria-hidden="true"></div>',
     unsafe_allow_html=True,
 )