Bug reports aren’t generally considered using custom CSS. Your clip also isn’t using the default theme.
Custom theme and snippets: for cosmetic issues, please first try updating your theme and disabling your snippets. If still not fixed, please try to make the issue happen in the Sandbox Vault or disable community theme and snippets.
You can use something like this to restrict the CSS to only notes:
.workspace-leaf-content[data-type="markdown"] img {
width: 350px;
}