Thomas Williams shares a few tips:
In this post I go over some low-effort ways to improve controls to save space, offer missing functionality, and better help end users. See the file https://github.com/thomasswilliams/r-markdown-snippets/blob/main/improve-inputs-1.Rmd for the full source code in a ready-to-run R Markdown file (all you need is R and RStudio).
Click through for several examples.