Common built-in themes for use with the theme argument in surveyjs() as documented on surveyjs - Themes & Styles every theme comes with a light & dark version and once with and without panels.
Examples
surveyjs_themes()
#> [1] "BorderlessDark" "BorderlessDarkPanelless"
#> [3] "BorderlessLight" "BorderlessLightPanelless"
#> [5] "ContrastDark" "ContrastDarkPanelless"
#> [7] "ContrastLight" "ContrastLightPanelless"
#> [9] "DefaultDark" "DefaultDarkPanelless"
#> [11] "DefaultLight" "DefaultLightPanelless"
#> [13] "DoubleBorderDark" "DoubleBorderDarkPanelless"
#> [15] "DoubleBorderLight" "DoubleBorderLightPanelless"
#> [17] "FlatDark" "FlatDarkPanelless"
#> [19] "FlatLight" "FlatLightPanelless"
#> [21] "LayeredDark" "LayeredDarkPanelless"
#> [23] "LayeredLight" "LayeredLightPanelless"
#> [25] "PlainDark" "PlainDarkPanelless"
#> [27] "PlainLight" "PlainLightPanelless"
#> [29] "SharpDark" "SharpDarkPanelless"
#> [31] "SharpLight" "SharpLightPanelless"
#> [33] "SolidDark" "SolidDarkPanelless"
#> [35] "SolidLight" "SolidLightPanelless"
#> [37] "ThreeDimensionalDark" "ThreeDimensionalDarkPanelless"
#> [39] "ThreeDimensionalLight" "ThreeDimensionalLightPanelless"
#> [41] "__surveyjs_internal_themes_hash" "default"