Depending on the style rules and specificity of the CSS attached to a page, the components of the rich text module editor can appear distorted as it tries to follow the rules of the CSS. This is why some components like the buttons, fields, or labels in the rich text module editor can be affected.
For cases like these, work with the original designer of the stylesheets that are causing the conflict. The original designer will have context about the source of the conflict and the technical skills required to make any changes. HubSpot Designers Documentation offers guidelines for making sure your CSS/JS works in HubSpot's editors.