Allowing fullscreen in embedded Youtube video

[EricLi0480]

Hello everyone,
Here is my ui.R:

library(shiny)
library(shinyFiles)
library(bslib)
library(thematic)
library(shinydashboard)
set.seed(500)

ui <- dashboardPage(
  dashboardHeader(title = "My Course"),
  dashboardSidebar(
    sidebarMenu(
      menuItem("Unit 01: Introduction", tabName = "unit00"),
      menuItem("Unit 01: Input and Output", tabName = "unit01")
    )
  ),
  dashboardBody(
    tabItems(
      tabItem(
        tabName = "unit00",
        fluidRow(
          # Embed video
          box(
            title = "Watch the Lesson",
            tags$iframe(src="https://www.youtube.com/embed/2SU-sDbvsvA", 
                        frameborder="0", 
                        allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture")
          ),
          box()
        )
      )
    )
  )
)

There are two issues with my app. First, I'd like the size of the video to match the size of the box (in its current state, if the user makes the window bigger, the video box stays the same size, so it only fills up a small bit of the white box). Additionally, it appears that fullscreen has been disabled. How can I resolve these issues?

Thanks!