When using the Settings window to change Obsidian’s appearance (as in applying different themes, modifying existing themes, refreshing CSS snippets, or changing core appearance settings such as font size), it is currently impossible to see the effects of the changes in real-time. Instead, the user must exit the Settings window, evaluate what they see, and then re-enter Settings to make any further adjustments (sometimes having to navigate back down through several layers of settings to get back to the relevant spot).
This process is detrimental because (1) cycle time between making changes and evaluating their effects is long, and (2) there is a burden placed upon the user’s short-term memory regarding (a) what setting was changed and (b) how that change affected Obsidian’s appearance, since they can only see one of those at a time (and must mentally compare with the previous appearance, since they were unable to observe the change directly).
Since making the Settings window a truly separate window is apparently not feasible within Obsidian’s Electron framework (see this discussion), allowing the Settings window to be resizable would allow the user to dynamically move and adjust the window as needed to view the main user interface behind it and observe how changes in appearance affect the interface in real-time.
Currently no workarounds. Capturing and comparing static screenshots may be the best alternative to just repeated rounds of feedback-delayed guess-and-check attempts.