Silverbullet supports admonitions using GitHub syntax (note and warning).

note This is a
note admonition

warning This is a
warning admonition

Custom admonitions can be added in a Space Style using the following format:

// Replace the keyword with a word or phrase of your choice
.sb-admonition[admonition="keyword"] {
  .sb-admonition-type * { display: none; }
    // The icon can be a link or an embedded image like shown here
  --admonition-icon: url('data:image/svg+xml,<svg viewBox="0 0 24 24" fill="none" xmlns=""><g id="SVGRepo_bgCarrier" stroke-width="0"></g><g id="SVGRepo_tracerCarrier" stroke-linecap="round" stroke-linejoin="round"></g><g id="SVGRepo_iconCarrier"><path d="M19.5 12L14.5 17M19.5 12L14.5 7M19.5 12L9.5 12C7.83333 12 4.5 11 4.5 7" stroke="%231C274C" stroke-width="1.5" stroke-linecap="round" stroke-linejoin="round"></path></g></svg>');
  // The accent color
  --admonition-color: green;