Working.

static/main.css

@@ -5,6 +5,7 @@
 :root {
     --main-bg-color: white;
     --main-hover-color: rgb(64, 64, 64);
+    --post-hover-color: rgb(32,32,32);
     --border-color: rgb(132, 136, 138);
     --edge-color: rgb(60, 60, 60);
     --main-fg-color: black;
@@ -142,7 +143,7 @@ hr {
 }
 
 .post-body:hover {
-    background-color: var(--main-hover-color);
+    background-color: var(--post-hover-color);
 }
 
 #log {
@@ -316,7 +317,39 @@ iframe {
 }
 
 #compose-reply-area {
-    display:none;
+    display: none;
+    padding: 8px 10px;
+    margin-bottom: 8px;
+    border-left: 3px solid var(--highlight-fg-color);
+    font-size: 0.85em;
+}
+
+.compose-reply-preview {
+    display: flex;
+    gap: 10px;
+    align-items: flex-start;
+}
+
+.compose-reply-preview-text {
+    flex: 1;
+    overflow: hidden;
+    max-height: 80px;
+}
+
+.compose-reply-preview-text iframe {
+    width: 120px;
+    height: 68px;
+    pointer-events: none;
+}
+
+.compose-reply-preview-image {
+    width: 48px;
+    height: 48px;
+    max-width: 48px;
+    max-height: 48px;
+    object-fit: cover;
+    border-radius: 4px;
+    flex-shrink: 0;
 }
 
 .show {