Preview Refreshing: Live vs. On-Save
Whenever possible, Previews in Coda will refresh live, on-the-fly as you edit the previewed file. However some types of files can only update their previews when you save.
Static pages (.html) update on-the-fly, both locally and remotely.
Dynamic pages (such as .php or containing server-side includes) must be parsed by the server, and thus require saving before the preview can be updated.
CSS files (.css) must be previewed via a separate page that imports the CSS via an @import directive or <link> tag. The preview will update when you save the CSS file.