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/AVvXsEjsgUE-jBQ37DW8x7h-3j0-DP2F2_IleUIv_rdKcUGMV4LWF9T-4M6wvOnjrunU5SlZsvOTwupCak62GNsZsh0tQPPR_o9yu1-9j7hja1gyNf0FyAz3Z40_0lRGU_SSaePCPYHZRGu9KrE/s1600/sidebarli.jpg) no-repeat scroll left center;
=> You can change the image URL, with your choice5. Save now.