full text vs summary in blogsmu theme

Good morning! Hope you all are well! I want to show a summary of posts on blog page in blogsmu theme. This question is actually answered in this thread:

https://premium.wpmudev.org/forums/topic/my-blog-page-shows-entire-post-instead-of-summary

Can I use the code sited in this post in the "my css plugin" to accomplish the same thing? If not, do you have a snippet of code that I could insert in that plugin to get a summary instead of full text? Thanks in advance! Linda @iempoweru