Hi @randomnameee,
The URL that you have provided about the tweet does not have anything to do with your original question regarding the Vimeo:
I am not sure how you embedded the Twitter if you used a third party plugin you need to contact the plugin developer. The embedded code is not related to our theme. You can test that by changing the theme to default WordPress theme and try to embed the Twitter code, and you will have the same result.
Now regarding this link:
http://www.desmondchan.org/the-all-american-athletes/
The problem that you are experiencing is because you added a Custom CSS to limit all the iFrames in the page. The code is:
.entry-content iframe {
min-width: 500px;
max-width: 550px;
}
Please go to Appearance > Customize > Custom CSS and remove that code.
It is worth to mention that you are using a super old version of the theme which can not be supported anymore. You need to back up your website thoroughly and update the theme and Cornerstone to the latest version. Unfortunately, it is not possible to give proper support for version 4.0.6 of the theme which is super old.
Thank you.