QT Material Theme OS Default on Startup Instability

[JackEAllen]

Summary

If the Mantid Imaging theme is set to anything other than Fusion on startup, when "Use OS Default" is selected, The Theming of select widgets and windows can get a little muddled.

This can be resolved by selecting the Fusion theme and restarting Mantid Imaging.

There is likely a variable somewhere on startup that does not validate the theme in use.

Explore the cause and implement a fix. - A few possible solutions may include modifying the CSS stylesheets or setting sizing policies.

Steps To Reproduce

• Start Mantid Imaging
• Select File > Settings
• Select an alternative theme to Fusion
• Restart mantid Imaging
• Select File > Settings
• Select "Use OS Default"

The theming should look a little strange.

Expected Behaviour

Mantid Imaging should be able to perform Theme validation on startup to ensure themes don't get muddled together.

Current Behaviour

Themes can become unstable on startup if not set to Fusion.

Context

Bug found during testing.

Failure Logs

Screenshot(s)

Fusion when fusion loaded in on startup:

When loading Mantid Imaging with qt material theme: