fix(office): align ppt preview chrome spacing

Co-authored-by: Codex (GPT 5.5) <codex@openai.com>

Author: phodal

src/app/debug/office-wasm-poc/presentation-preview.module.css

@@ -84,13 +84,13 @@
 }
 
 .thumbnailButton[data-active="true"] .thumbnailCanvas {
-  box-shadow: none;
+  box-shadow: 0 0 0 2px #60a5fa;
 }
 
 .thumbnailButton[data-active="true"] {
-  background: #ffffff;
-  border-color: #60a5fa;
-  box-shadow: 0 0 0 1px rgba(96, 165, 250, 0.45);
+  background: transparent;
+  border-color: transparent;
+  box-shadow: none;
 }
 
 .mainPanel {
@@ -125,6 +125,7 @@
   align-items: stretch;
   background: #f8fafc;
   display: flex;
+  flex-direction: column;
   justify-content: center;
   min-height: 0;
   min-width: 0;
@@ -137,7 +138,8 @@
 .viewport {
   align-items: center;
   display: flex;
-  height: 100%;
+  flex: 1 1 auto;
+  height: auto;
   justify-content: center;
   min-height: 0;
   min-width: 0;
@@ -225,24 +227,23 @@
 }
 
 .footnote {
+  align-self: center;
   background: #ffffff;
   border: 1px solid #eef2f7;
   border-radius: 8px;
   box-shadow: 0 10px 26px rgba(15, 23, 42, 0.08);
   box-sizing: border-box;
-  bottom: 14px;
   color: #64748b;
   font: 12px/1.6 var(--font-sans, -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", sans-serif);
-  left: 50%;
-  margin: 0;
+  margin: 14px 0 0;
   max-height: 96px;
   max-width: calc(100% - 48px);
   overflow: auto;
   padding: 12px 14px;
-  position: absolute;
-  transform: translateX(-50%);
+  position: static;
+  transform: none;
   white-space: pre-wrap;
-  z-index: 4;
+  z-index: 1;
 }
 
 .slideshowOverlay {