Are you running into the following error

Encoding::UndefinedConversionError - "\xE2" from ASCII-8BIT to UTF-8:

If you are using Ruby and SASS for your stylesheets then it might help to start your stylesheets with:

@charset "UTF-8"

In my main sinatra app I had

before do
  content_type 'text/html', :charset => 'utf-8'
end

get '/base.css' do
  sass :'stylesheets/base'
end

Now the before route forces it to be utf-8 so stylesheets/base.sass also needs a charset defining:

@charset "UTF-8"

body
  font:
    family: Helvetica, Arial, sans-serif

#head
  margin: 0
  padding: 1em
  background-color: #ccc