style: fix layout structure for proper sticky header and footer

- Fix flexbox layout to use min-height: 100vh instead of height
- Make sidebar sticky positioned
- Ensure header and footer are fixed while content scrolls
- Simplify content area without forced height constraints

Author: loveTsong

assets/css/style.css

@@ -13,12 +13,14 @@ body {
   line-height: 1.6;
   color: #24292e;
   background-color: #f6f8fa;
+  min-height: 100vh;
   display: flex;
   flex-direction: column;
 }
 
 .wrapper {
   max-width: 1200px;
+  width: 100%;
   margin: 0 auto;
   padding: 0 16px;
   flex: 1;
@@ -30,6 +32,7 @@ body {
   background-color: #24292e;
   color: #fff;
   padding: 16px 0;
+  flex-shrink: 0;
 }
 
 .site-title {
@@ -59,22 +62,20 @@ body {
 .page-content {
   padding: 32px 0;
   flex: 1;
-  display: flex;
-  flex-direction: column;
 }
 
 .page-content .wrapper {
   display: flex;
   gap: 32px;
-  flex: 1;
-  min-height: 0;
+  height: 100%;
 }
 
 .sidebar {
   width: 260px;
   flex-shrink: 0;
-  overflow-y: auto;
-  max-height: calc(100vh - 200px);
+  align-self: flex-start;
+  position: sticky;
+  top: 0;
 }
 
 .content {
@@ -84,8 +85,6 @@ body {
   padding: 24px;
   border-radius: 6px;
   box-shadow: 0 1px 3px rgba(0,0,0,0.12);
-  overflow-y: auto;
-  max-height: calc(100vh - 200px);
 }
 
 .content h1 {
@@ -166,6 +165,7 @@ body {
   color: rgba(255,255,255,0.7);
   padding: 24px 0;
   text-align: center;
+  flex-shrink: 0;
 }
 
 .site-footer p {