Alpha < 1 in background color no longer works in column_spec()

[fornaeffe]

Describe the bug
Until a few days ago, all worked fine. Since yesterday (maybe after an update of some packages) colors specified by column_spec( background = "...") are rendered fully opaque even if I specify alpha < 1.

To Reproduce

---
title: "Test"
format: html
---


```{r}
library(kableExtra)

df <- data.frame(
  column1 = c("cell1", "cell2"),
  column2 = c("cell3", "cell4")
)

kbl(df, "html") %>%
  kable_minimal() %>%
  column_spec(1, background = "#00FF0010")
```

This is my session info:

R version 4.4.1 (2024-06-14 ucrt)
Platform: x86_64-w64-mingw32/x64
Running under: Windows 11 x64 (build 22631)

Matrix products: default


locale:
[1] LC_COLLATE=Italian_Italy.utf8  LC_CTYPE=Italian_Italy.utf8    LC_MONETARY=Italian_Italy.utf8
[4] LC_NUMERIC=C                   LC_TIME=Italian_Italy.utf8    

time zone: Europe/Rome
tzcode source: internal

attached base packages:
[1] stats     graphics  grDevices utils     datasets  methods   base     

other attached packages:
[1] kableExtra_1.4.0

loaded via a namespace (and not attached):
 [1] vctrs_0.6.5       svglite_2.1.3     cli_3.6.2         knitr_1.47        rlang_1.1.4      
 [6] xfun_0.45         stringi_1.8.4     highr_0.11        pkgload_1.3.4     formattable_0.2.1
[11] jsonlite_1.8.8    glue_1.7.0        colorspace_2.1-0  htmltools_0.5.8.1 sass_0.4.9       
[16] scales_1.3.0      rmarkdown_2.27    jquerylib_0.1.4   evaluate_0.24.0   munsell_0.5.1    
[21] fastmap_1.2.0     lifecycle_1.0.4   stringr_1.5.1     compiler_4.4.1    htmlwidgets_1.6.4
[26] rstudioapi_0.16.0 systemfonts_1.1.0 digest_0.6.35     viridisLite_0.4.2 R6_2.5.1         
[31] parallel_4.4.1    magrittr_2.0.3    bslib_0.7.0       tools_4.4.1       cachem_1.1.0     
[36] xml2_1.3.6 

[dmurdoch]

Your document looks like a Quarto document. Is it?

[fornaeffe]

Yes it is

[dmurdoch]

That may be your problem. kableExtra was written for R Markdown. It's gradually being adapted to also work with Quarto, but that work is not complete. Since kableExtra hasn't had a release since January, it's likely a Quarto change (or some other package) that caused the issue.