R: fill down multiple columns

I'm using fill() from the tidyr package. fill(df, colname1, colname2, colname3) works fine, until I found a dataset with 32 variables. How should I fill down all columns without typing each name?

I've tried:

fill(df,colnames(df)),
fill(df,1:32), 
fill(df,colname1:colname32). 

All gives the same error:

Error: All select() inputs must resolve to integer column positions.
The following do not:
*  colnames(df1)

We can use fill_

fill_(df, names(df))