refactor: switch header from fixed to sticky, remove compensating offsets

Fixed positioning required padding-top on every page container to avoid
content going under the header. Sticky keeps the header in flow so those
offsets are no longer needed.

Author: Kevin Allioli

static/style.css

@@ -84,8 +84,8 @@ body {
 
 /* ── Header ─────────────────────────────────────────────────────────────────── */
 header {
-  position: fixed;
-  top: 0; left: 0; right: 0;
+  position: sticky;
+  top: 0;
   z-index: 100;
   height: 70px;
   display: flex;
@@ -157,11 +157,10 @@ header {
 /* ── Index page layout ──────────────────────────────────────────────────────── */
 .index-layout {
   flex: 1;
-  height: 100vh;
+  height: calc(100vh - 70px);
   overflow: hidden;
   display: flex;
   flex-direction: column;
-  padding-top: 70px;
 }
 
 .index-hero {
@@ -683,7 +682,7 @@ kbd {
 }
 
 .paste-layout {
-  padding-top: 98px;
+  padding-top: 28px;
   max-width: 1100px;
   margin: 0 auto;
   padding-left: 32px;
@@ -1220,7 +1219,7 @@ kbd {
   .header-actions { gap: 6px; }
 
   /* ── Index layout: scrollable instead of fixed 100vh ── */
-  .index-layout { height: auto; min-height: 100vh; overflow: visible; padding-top: 54px; }
+  .index-layout { height: auto; min-height: calc(100vh - 54px); overflow: visible; }
   /* ── Form ── */
   .index-form { flex-direction: column; padding: 20px 12px 24px; flex: none; gap: 20px; }
   .index-sidebar { flex: none; width: 100%; gap: 20px; }
@@ -1246,7 +1245,7 @@ kbd {
   .site-footer { display: block; text-align: center; padding: 12px 16px; line-height: 2; }
 
   /* ── Paste page ── */
-  .paste-layout { padding-top: 60px; padding-left: 14px; padding-right: 14px; padding-bottom: 30px; }
+  .paste-layout { padding-top: 16px; padding-left: 14px; padding-right: 14px; padding-bottom: 30px; }
   .line-gutter { padding: 10px 8px 10px 10px; min-width: 44px; font-size: 0.8rem; }
   .paste-body pre { padding: 10px 12px; font-size: 0.82rem; }
   .paste-inbar { flex-direction: row; align-items: center; flex-wrap: wrap; gap: 6px; }