An example of showing a desired arrangement for html widgets

rmarkdown_htmlwidget_arrange.Rmd

---
title: "R Notebook"
output:
  pdf_document: default
  html_notebook: default
---

###Default Arrangement
```{r, echo=FALSE,message=FALSE}
# devtools::install_github("wch/webshot")
library(leaflet)
library(htmltools)
library(RColorBrewer)

m1 <- leaflet(quakes) %>% 
        addTiles() %>% 
        addMarkers(lng=174.768, lat=-36.852)

m2 <- leaflet(quakes) %>% 
        addProviderTiles("Esri.WorldGrayCanvas") %>% 
        addMarkers(lng=174.768, lat=-36.852)

m3 <- leaflet(quakes) %>%
        addProviderTiles("Stamen.Toner") %>%
        addMarkers(lng=174.768, lat=-36.852)

m1
m2
m3

```

###HTML Arrangement
```{r, echo=FALSE,message=FALSE}

browsable(
  tagList(list(
    tags$div(
      style = 'width:30%;display:block;float:left;padding:3px;',
      m1
    ),
    tags$div(
      style = 'width:30%;display:block;float:left;padding:3px;',
      m2
    ),
    tags$div(
      style = 'width:30%;display:block;float:left;padding:3px;',
      m3
    )
  ))
)

```