"At the same place" as yoga/index.html means that the template is actually yoga/base.html.
yoga/index.html
yoga/base.html
Assuming TEMPLATE_DIRS contains /home/mo/python/django/templates/, without the .../yoga/, so you need to:
/home/mo/python/django/templates/
.../yoga/
move base.html into /home/mo/python/django/templates/
base.html
OR
write {% extends "yoga/base.html" %} in your template
{% extends "yoga/base.html" %}
Is base.html in a directory in the TEMPLATE_DIRS list in your settings file?