Restore .lt-main.lt-container combined selector — proper cascade fix

The TDS v1.2 sync removed the .lt-main.lt-container combined selector that
was already in the project's base.css. That selector has specificity (0,2,0)
vs single-class (0,1,0), so it always wins over .lt-container padding
shorthand at every breakpoint without needing per-breakpoint overrides.

Also restored flex:1, width:100%, min-width:0 on .lt-main that were dropped.
Removed the incorrect per-breakpoint .lt-main and #main-content hacks added
today which were the wrong approach to the same problem.

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

assets/css/base.css

@@ -350,22 +350,17 @@ hr {
 
 .lt-main {
   padding-top: calc(var(--header-height) + var(--space-lg));
+  flex: 1;
+  width: 100%;
+  min-width: 0;
 }
-
+/* When both lt-main and lt-container are on the same element, the lt-container
-/* ID selector (specificity 1,0,0,0) beats any class combination — guarantees
+   shorthand `padding` overrides the lt-main `padding-top` in responsive breakpoints
-   the fixed header never overlaps content regardless of cascade order. */
+   (same cascade specificity, later rule wins). The combined selector has higher
-#main-content {
+   specificity (0,2,0 vs 0,1,0) and always wins regardless of source order. */
+.lt-main.lt-container {
   padding-top: calc(var(--header-height) + var(--space-lg));
 }
-@media (max-width: 1023px) {
-  #main-content { padding-top: calc(var(--header-height) + var(--space-md)); }
-}
-@media (max-width: 767px) {
-  #main-content { padding-top: calc(50px + var(--space-md)); }
-}
-@media (max-width: 479px) {
-  #main-content { padding-top: calc(46px + var(--space-sm)); }
-}
 
 .lt-layout {
   display: flex;
@@ -2023,8 +2018,6 @@ select option:checked {
 @media (max-width: 1279px) {
   .lt-grid-4 { grid-template-columns: repeat(2, 1fr); }
   .lt-container { padding: var(--space-lg); }
-  /* Restore header clearance after lt-container shorthand overrides padding-top */
-  .lt-main { padding-top: calc(var(--header-height) + var(--space-lg)); }
 }
 
 
@@ -2036,8 +2029,6 @@ select option:checked {
   .lt-grid-3, .lt-grid-4 { grid-template-columns: repeat(2, 1fr); }
   .lt-stats-grid { grid-template-columns: repeat(2, 1fr); }
   .lt-container { padding: var(--space-md) var(--space-lg); }
-  /* Restore header clearance after lt-container shorthand overrides padding-top */
-  .lt-main { padding-top: calc(var(--header-height) + var(--space-md)); }
   .lt-header { padding: 0 var(--space-lg); }
 
   /* Sidebar becomes off-canvas on tablets */
@@ -2062,8 +2053,6 @@ select option:checked {
 @media (max-width: 767px) {
   :root { --header-height: 50px; }
   .lt-container { padding: var(--space-md); }
-  /* lt-main must come after lt-container so padding-top isn't clobbered by the shorthand */
-  .lt-main { padding-top: calc(50px + var(--space-md)); }
   .lt-header { padding: 0 var(--space-md); }
   .lt-brand-subtitle { display: none; }
 
@@ -2162,8 +2151,6 @@ select option:checked {
 @media (max-width: 479px) {
   :root { --header-height: 46px; }
   .lt-container { padding: var(--space-sm); }
-  /* lt-main must come after lt-container so padding-top isn't clobbered by the shorthand */
-  .lt-main { padding-top: calc(46px + 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; }
@@ -2260,8 +2247,6 @@ select option:checked {
   .lt-stats-grid { grid-template-columns: repeat(6, 1fr); }
   .lt-grid-4 { grid-template-columns: repeat(4, 1fr); }
   .lt-container { padding: var(--space-xl) var(--space-2xl); }
-  /* Restore header clearance after lt-container shorthand overrides padding-top */
-  .lt-main { padding-top: calc(var(--header-height) + var(--space-xl)); }
 }