The size of all the texts in the attachment widget to the size of the text in the document. In Adobe Muse, the text size of the documents is always 14px.
The font size of all the texts of the widget is 1em = 14px
You can reduce and enlarge the font size of the document text. To do this, add this CSS code to the Page property
<style> html, body{ font-size: 16px; /* New font size */ } </style>
In order to do this, follow the next steps:
Step 1
Right click on the page, and select Page properties

Step 2
Select the Metadata tab, and insert the code for customization in the field HTML for <head>
Also, you can fine-tune each type of text using CSS, more in this article