1. Log in to your blogger account
2. Go to Design --> Edit HTML
3. Find this code : .
.sidebar ul li {
4. Then add the code below, under .sidebar ul li {background:transparent url(https://blogger.googleusercontent.com/img/b/R29vZ2xl/AVvXsEj9e0PboNB1arVtkww-ozrHvbGb8KjU83rOP9a5dwd69tmXGiEq929nSGzqKHwMcjp0JGeCmE8pms-vBe6gTyWg4MolU1Ls6iNOj6vMrbUhaTOWjal060XWQ8iUC8c6-KAyt-kgOLyzHDM/s1600/sidebarli.jpg) no-repeat scroll left center;
=> You can change the image URL, with your choice5. Save now.