feat: improve theme contrast and button styling

Enhanced the Pivoine theme with better visual hierarchy and usability:

Logo improvements:
- Fixed logo selector to target .navbar-brand img (not just .logo)
- Logo now properly colorized with primary rose/magenta color

Contrast improvements:
- Changed body background to darker shade (bg-darker)
- Added main content area with lighter background (bg-dark) for better separation
- Added heading styles with rose accent color
- H1/H2 headings now have rose bottom border for visual hierarchy

Button refinements:
- Split button styling into primary buttons and filter buttons
- Filter buttons (.btn-light in .btn-group) now have subtle, elegant styling:
  * Lighter background with border
  * Smaller size and lighter font weight
  * Hover shows rose border and text color
  * Active state has solid rose background
- Primary buttons maintain bold rose background styling

The result is clearer visual separation between navigation, content, and
interactive elements with better contrast throughout.

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

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

asciinema/theme/custom.css

@@ -35,11 +35,34 @@
 
 /* Global Styling */
 body {
-  background-color: var(--pivoine-bg-dark) !important;
+  background-color: var(--pivoine-bg-darker) !important;
   color: var(--pivoine-text-primary) !important;
   font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Helvetica Neue", Arial, sans-serif !important;
 }
 
+/* Main content area with better contrast */
+main,
+.main-content {
+  background-color: var(--pivoine-bg-dark) !important;
+  min-height: 100vh;
+}
+
+/* Headings with accent color */
+h1, h2, h3, h4, h5, h6,
+.h1, .h2, .h3, .h4, .h5, .h6 {
+  color: var(--pivoine-text-primary) !important;
+}
+
+h1, h2, .h1, .h2 {
+  border-bottom: 2px solid var(--pivoine-rose) !important;
+  padding-bottom: 8px !important;
+  margin-bottom: 16px !important;
+}
+
+.heading h2 {
+  color: var(--pivoine-rose-light) !important;
+}
+
 /* Header & Navigation */
 header,
 .header,
@@ -81,9 +104,8 @@ a:focus {
   text-decoration: underline;
 }
 
-button,
-.btn,
-.btn-light,
+/* Primary buttons and submit buttons */
+button:not(.btn-light):not(.btn-group .btn),
 input[type="submit"] {
   background-color: var(--pivoine-rose) !important;
   color: white !important;
@@ -96,28 +118,49 @@ input[type="submit"] {
   box-shadow: 0 2px 4px rgba(0, 0, 0, 0.2);
 }
 
-button:hover,
-.btn:hover,
-.btn-light:hover,
+button:not(.btn-light):not(.btn-group .btn):hover,
 input[type="submit"]:hover {
   background-color: var(--pivoine-rose-light) !important;
   box-shadow: 0 4px 8px var(--pivoine-rose-glow);
   transform: translateY(-1px);
 }
 
-button:active,
-.btn:active,
-.btn-light:active,
+button:not(.btn-light):not(.btn-group .btn):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,
+/* Filter buttons (btn-light in btn-group) */
+.btn-group .btn,
+.btn-light {
+  background-color: var(--pivoine-bg-lighter) !important;
+  color: var(--pivoine-text-primary) !important;
+  border: 1px solid var(--pivoine-border) !important;
+  border-radius: 4px !important;
+  padding: 6px 14px !important;
+  font-weight: 500 !important;
+  font-size: 0.9em !important;
+  cursor: pointer;
+  transition: all 0.2s ease;
+  box-shadow: none !important;
+}
+
+.btn-group .btn:hover,
+.btn-light:hover {
+  background-color: var(--pivoine-bg-dark) !important;
+  border-color: var(--pivoine-rose) !important;
+  color: var(--pivoine-rose-light) !important;
+  transform: none !important;
+}
+
+/* Active state for filter buttons */
+.btn-group .btn.active,
 .btn-light.active {
-  background-color: var(--pivoine-rose-dark) !important;
+  background-color: var(--pivoine-rose) !important;
+  border-color: var(--pivoine-rose) !important;
   color: white !important;
+  font-weight: 600 !important;
 }
 
 /* Cards & Containers */
@@ -424,6 +467,7 @@ code {
 }
 
 /* Logo & Branding */
+.navbar-brand img,
 .logo {
   filter: brightness(0) saturate(100%) invert(47%) sepia(74%) saturate(1845%) hue-rotate(319deg) brightness(93%) contrast(87%);
 }