You are asking very strange question. Base64 is for encoding a binary data while .svg is just a file type for vector graphics for the web in a simple HTML-like style.
I even will copy a direct definition of Base64 from Wikipedia (or Wikiwand extension in my case which adds awesome UI to Wikipedia).
So Base64 is a group of similar binary-to-text encoding schemes that represent binary data in an ASCII string format. You can encode any data you want to Base64: text, styles, images, including svg. Historically it was invented for email attachements to support them on any machines and protocols. Today it is used to inline small assets into HTML to avoid a lot of extra HTTP requests. Answer here from historical point of view is very long and I will just leave these two good answers on StackOverflow: