I've answered your question in this topic: https://feedback.textasticapp.com/communities/1/topics/1333-linking-html-and-css-files

Hello,

make sure to store your HTML, CSS and JS files somewhere in "Local Files", "iCloud" or in a folder added using "Add External Folder…". 

You can link to your CSS file using a "link" tag in the HTML file's head section like this:

<link rel="stylesheet" href="example.css">

Similarly, you can link an external JavaScript file like this:

<script src="myscript.js"></script>

If you then preview the HTML file using the "glasses" icon, the CSS and JavaScript file should be loaded.

Please have a look at these topics in the manual for details:

https://www.textasticapp.com/v10/manual/managing_files/local_files_icloud.html

https://www.textasticapp.com/v10/manual/viewing_editing_files/web_preview.html

https://www.textasticapp.com/v10/manual/integration_other_apps/external_files_folders.html#adding-external-folders

Note: The web preview cannot load the referenced files if you opened a single HTML file from the Files app using Textastic's "Open…" command since that only gives Textastic access to the single file you selected and not to its containing folder.

Regarding the iCloud Documents folder: you can use the "Add External Folder" command to add the iCloud documents folder to Textastic. See https://www.textasticapp.com/v10/manual/integration_other_apps/external_files_folders.html

Textastic 10.4.1 ships with a new version of libcurl which fixes problems with uploading files to FTPS servers using TLS 1.3. The workaround to set the maximum TLS version to 1.2 is no longer necessary.

The problem was an improper shutdown of the TLS connection after the upload. As a result, the server rejected the uploaded data. See https://github.com/curl/curl/pull/13904 for details.

If the same document in iCloud Drive is edited on two devices, those changes should already be synced and the editor should update.

If the document is changed on both devices, the document should be in a conflict state and Textastic should present a conflict resolution dialog. 

Is that not what you are seeing?

Sometimes it can take a while for iCloud Drive to actually sync changes. That's out of my control.

I'm glad that it worked! 

I believe that the latest version of libcurl includes a fix for this issue and I hope to update Textastic soon with this new version so that this workaround will no longer be necessary. 

The problem is that TLS 1.3 connections are not shut down properly after the upload finishes, so some FTPS servers reject the uploaded file.

There is a known problem with uploads to some servers when using FTPS connections. 

Are you sure this is an SFTP connection and not an FTPS connection?

From the release notes of Textastic 10.3.2:

Textastic uses libcurl to transfer files to FTPS servers. On some FTPS servers, uploading a file with curl when using TLS 1.3, if the file is larger than about 18 KB, may result in a "partial upload" error and a 0-byte file on the server.

To work around this partial file upload issue, you can reduce the maximum TLS version to 1.2.

Note: This is only relevant for FTPS connections. SFTP connections are not affected.

This issue has also been reported to the curl project and will hopefully be fixed in a future update of the library. In the meantime, you can use this workaround.

So, if this is indeed an FTPS connection, please try to set the maximum TLS version to 1.2 in the connection's settings and see if this helps.

Thanks for the feedback! I'll consider adding a replace option in the future. I'm glad you're enjoying the app!