fix: target Bootstrap-specific classes in custom theme

Updated custom.css to target the actual Bootstrap classes used by
asciinema server instead of generic selectors:

- Added .navbar-dark and .bg-dark overrides for navigation
- Added .btn-light targeting for button styles
- Added .btn.active and .btn-light.active for active button states

This ensures the Pivoine theme properly overrides Bootstrap's default
dark theme classes.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

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

asciinema/theme/custom.css

@@ -43,11 +43,18 @@ body {
 /* Header & Navigation */
 header,
 .header,
-nav {
+nav,
+.navbar {
   background-color: var(--pivoine-bg-darker) !important;
   border-bottom: 2px solid var(--pivoine-rose) !important;
 }
 
+/* Override Bootstrap navbar-dark and bg-dark */
+.navbar-dark,
+.bg-dark {
+  background-color: var(--pivoine-bg-darker) !important;
+}
+
 .navbar,
 .nav-link {
   color: var(--pivoine-text-primary) !important;
@@ -76,6 +83,7 @@ a:focus {
 
 button,
 .btn,
+.btn-light,
 input[type="submit"] {
   background-color: var(--pivoine-rose) !important;
   color: white !important;
@@ -90,6 +98,7 @@ input[type="submit"] {
 
 button:hover,
 .btn:hover,
+.btn-light:hover,
 input[type="submit"]:hover {
   background-color: var(--pivoine-rose-light) !important;
   box-shadow: 0 4px 8px var(--pivoine-rose-glow);
@@ -98,11 +107,19 @@ input[type="submit"]:hover {
 
 button:active,
 .btn:active,
+.btn-light:active,
 input[type="submit"]:active {
   transform: translateY(0);
   box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
 }
 
+/* Active state for buttons */
+.btn.active,
+.btn-light.active {
+  background-color: var(--pivoine-rose-dark) !important;
+  color: white !important;
+}
+
 /* Cards & Containers */
 .card,
 .panel,