Theme: set header brand color and constrain downloads dropdown to viewport

[Copilot]

This updates the supplemental UI theme to use rgb(0, 183, 191) for the header background and improves the downloads dropdown layout so it does not overflow the browser frame.

• Header theming

  • Applied the target brand color to the top navigation container in supplemental UI styles.

• Downloads dropdown containment

  • Anchored the downloads menu to the right edge of its trigger container.
  • Added a viewport-aware width cap so the menu remains visible on narrow screens while preserving existing desktop sizing behavior.

.header,
.navbar {
  background-color: rgb(0, 183, 191);
}

.downloads-dropdown-menu {
  min-width: 20rem;
  left: auto;
  right: 0;
  max-width: min(24rem, calc(100vw - 1rem));
}

[Copilot]

Pull request overview

Updates the Antora supplemental UI theme to align the header with the target brand color and prevent the downloads dropdown from overflowing the viewport in desktop layouts.

Changes:

• Set .header / .navbar background color to rgb(0, 183, 191).
• Right-align the downloads dropdown and cap its width based on the viewport using min().

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