Mở file .src/templates/blog-post.js sửa và thêm:

// src/templates/blog-post.js

import React from "react"
import Layout from "../components/layout"

import slug from "slug"
import { graphql, Link } from "gatsby"

import NavBar from "./navbar"
import SEO from "../components/seo/Seo"

..............

               {post.frontmatter.category ? (
                     <ul id="breadcrumbs" typeof="BreadcrumbList" vocab="http://schema.org/">
                        <li property="itemListElement" typeof="ListItem"> <Link to="/" property="item" typeof="WebPage"><span property="name">Home</span></Link><meta content="1" property="position" /></li> ›
                         {post.frontmatter.category.map(cat => (
                        <li class="breadcrumb-item" property="itemListElement" typeof="ListItem">
                          <Link to={`/${slug(cat).toLowerCase()}/`}  property="item" typeof="WebPage"><span property="name">{cat}</span></Link><meta content="2" property="position" />
                         </li>
                          ))}
                    </ul>
                    ) : null}

                <h1>{post.frontmatter.title}</h1>

                ...................