Vignettes don't look for pkg source code files

vignettes/css-help.Rmd

   comment = "#>"
 )
 
-source("../R/theme_settings.R")
+template_variables <- xaringanthemer:::template_variables
 ```
 
 Jump to: [Colors](#colors), [Sizes](#sizes), [Positioning](#positioning)

vignettes/singles/fonts.Rmd

 [adding-custom-css]: xaringanthemer.html#adding-custom-css
 
 ```{r, results='asis', echo=FALSE}
-source(here::here("R/theme_settings.R"))
-tvv <- template_variables$variable
+tvv <- xaringanthemer:::template_variables$variable
 ```
 
 ```{r child="../../man/fragments/_fonts.Rmd"}

vignettes/template-variables.Rmd

 For example, to use `mono_accent()` with a different slide background color, you can call `mono_accent(background_color = "#abc123")`.
 
 ```{r table, results = "asis", echo=FALSE}
-source("../R/theme_settings.R")
+template_variables <- xaringanthemer:::template_variables
 template_variables$variable <- glue::glue_data(template_variables, "`{variable}`")
 template_variables$default <- gsub("[{}]", "", template_variables$default)
 template_variables <- template_variables[, c(

vignettes/xaringanthemer.Rmd

 Here are some of the `text_` theme options:
 
 ```{r, results='asis', echo=FALSE}
-source(here::here("R/theme_settings.R"))
-tvv <- template_variables$variable
+tvv <- xaringanthemer:::template_variables$variable
 cat(paste0("- `", tvv[grepl("^text_", tvv)][1:5], "`"), sep = "\n")
 cat("- *and more ...*")
 ```