hybrid plain text gmail messages via uBlock Origin

gmail.txt

! hybrid plain text gmail messages

! block images
||gm1.ggpht.com/$image,domain=mail.google.com,important
mail.google.com##img.CToWUd
!mail.google.com##.editable img

! remove blockquote nesting
mail.google.com##[data-message-id^="#msg"] blockquote:style(padding:0!important;margin: 0!important;border: none!important;)
!mail.google.com##.editable blockquote:style(padding:0!important;margin: 0!important;border: none!important;)

! fluid width
mail.google.com##[data-message-id^="#msg"] hr:style(width:100%!important;max-width:100%!important;)
mail.google.com##[data-message-id^="#msg"] table:style(width:100%!important;max-width:100%!important;)
mail.google.com##.editable hr:style(width:100%!important;max-width:100%!important;)
mail.google.com##.editable table:style(width:100%!important;max-width:100%!important;)

! decolorize text
mail.google.com##[data-message-id^="#msg"] *:not(a):style(color:initial!important;)
!mail.google.com##.editable *:not(a):style(color:initial!important;)

! neutralize fonts
mail.google.com##[data-message-id^="#msg"] *:style(font-family:Arial,Helvetica,sans-serif!important;font-size:small!important;line-height:1.5!important;)
!mail.google.com##.editable *:style(font-family:Arial,Helvetica,sans-serif!important;font-size:small!important;line-height:1.5!important;)

! ban annoying font-styles in paragraphs
mail.google.com##[data-message-id^="#msg"] p *:style(font-weight:normal!important;font-style:normal!important)
!mail.google.com##.editable p *:style(font-weight:normal!important;font-style:normal!important)

Editable settings are not recommend (off by default)