Text configuration
Hi @karimelmasri -- Are you familiar with the StoryMaps theme builder? If not, you can read more about it here: Tips on using the ArcGIS StoryMaps theme builder (esri.com)
When creating a theme you can choose from many different fonts. There are over a dozen natively available in theme builder, but you can also browse 1000+ fonts from Google Fonts and specify the font weights used by your theme. You can also set font colors for different styles of text.
Once you create a theme, you can apply it to a story in the Design panel. Then, in the story builder you can change a text block's style from a regular paragraph to a heading, subheading, large paragraph, or other styles that represent different sizes and appearances. You can also make any text selection bold, italic, or change its color using the toolbar that appears when you highlight text.
If the options described above don't meet your needs, please clarify what is missing and how you'd like to use any additional capabilities so we can consider your request.