Yes, you should be able to. Based on Esri Can I customize the caption text formatting for my tour points?, you can achieve this using the standard HTML tags in your captions.
This blog provide an example in code form
`<div style=”font-size:90%”>China | 220 BC | Qin, Ming Chinese</div> <br>
<p>Once called the “long walls,” the Great Wall extends over 5,500 miles,
from the Yellow Sea in the east to the Taklamakan Desert in the West. It was
so extensive, in fact, that new segments are still being revealed. Built for
transportation and customs control as much as for defense, the walls were
joined into a unified system under the Qin Dynasty in the 3rd century BC, but
most of the present-day remains were constructed during the Ming Dynasty in
the 14th century AD. Modern travelers can find the most iconic sections of
restored wall about two hours from Beijing.</p>
<br>
<div style=”font-size:90%; color:#a9a9a9">Image: Adapted from <a
href=”https://unsplash.com/photos/hB_nkwIw5f4" style=”color:#b3c7df”>William
Christen</a> (Unsplash).</div>`
Yes. You can use standard HTML tags to format the text in your captions and also add hyperlinks. For example, this Map Tour uses HTML tags to format the caption text and add a hyperlink to a website. If you add hyperlinks, be sure to use the target="blank" parameter so that your target link opens in a new tab, so your readers can return to your tour by closing that tab without losing their place. See this blog post about adding HTML formatting and links to Story Map Tour captions. You can also use HTML tags to format the title and subtitle of a Map Tour.
For security reasons, ArcGIS only allows a specific set of HTML tags to be used. In the Story Map Tour Builder if you add unsupported HTML tags into the tour title, names or captions, you'll either see the tags simply appear as text, or the builder may give you the error message "Save failed due to an invalid html tag in a name or description" when you press Save (in which case you'll need to remove the unsupported tag in order to save). Here is the standard list of supported HTML. Story Map Tour also supports the hr tag to get a horizontal ruler line in a caption. like in the example above. However note that if you are using the option to upload images into the Story Map Tour, there are additional restrictions on the supported HTML you can use in a tour because that option uses a feature service.
For feature services see this standard list of supported HTML. The hr tag is not supported in Map Tours that use uploaded images, however you can use a div tag set to style="border-top:1px solid #000" to get a horizontal ruler (supported in Side Panel layout only). Similarly, the audio tag to embed audio clips in Map Tour captions is not supported in Map Tours that use uploaded images (see this blog post about adding audio to Map Tour).
