How do I add a sidebar to my Squarespace blog?

Squarespace 7.1 doesn't have a built-in blog sidebar, but you can create one by adding a code block or summary block next to your blog content and using CSS grid to create a two-column layout.

The approach: add a section below your blog with sidebar content (categories, recent posts, about), then use CSS to reposition it beside the blog feed. Wrap the blog section in a grid container via CSS.

/* Make the blog section a two-column grid */
.blog-item-wrapper {
  display: grid !important;
  grid-template-columns: 1fr 300px !important;
  gap: 40px !important;
  max-width: 1200px;
  margin: 0 auto;
}

/* Sidebar stacks below on mobile */
@media screen and (max-width: 767px) {
  .blog-item-wrapper {
    grid-template-columns: 1fr !important;
  }
}