Add responsive .lt-main.lt-container overrides to match production base.css

Production base.css has per-breakpoint .lt-main.lt-container rules that
explicitly set padding-top with tighter spacing at SM/XS viewports. Adding
these to beta to match — ensures header clearance is bulletproof at all sizes.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

assets/css/base.css

@@ -2053,6 +2053,7 @@ select option:checked {
 @media (max-width: 767px) {
   :root { --header-height: 50px; }
   .lt-container { padding: var(--space-md); }
+  .lt-main.lt-container { padding-top: calc(var(--header-height) + var(--space-md)); }
   .lt-header { padding: 0 var(--space-md); }
   .lt-brand-subtitle { display: none; }
 
@@ -2151,6 +2152,7 @@ select option:checked {
 @media (max-width: 479px) {
   :root { --header-height: 46px; }
   .lt-container { padding: var(--space-sm); }
+  .lt-main.lt-container { padding-top: calc(var(--header-height) + var(--space-sm)); }
   .lt-stats-grid { grid-template-columns: 1fr 1fr; gap: var(--space-xs); }
   .lt-stat-card { padding: var(--space-xs) var(--space-sm); }
   .lt-stat-value { font-size: 1.4rem; }