csscapture_py3: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/usr/bin/csscapture_py3 - from package: python3-cssutils

You may install the required package with command apt-get install {package}

Error in other languages:
csscapture_py3: bevel nie gevind nie
csscapture_py3: comandă negăsită
csscapture_py3: comando não encontrado
csscapture_py3: commande introuvable
csscapture_py3: command not found
csscapture_py3: käsku ei ole
csscapture_py3: không tìm thấy lệnh
csscapture_py3: komanda nerasta
csscapture_py3: Kommando nicht gefunden.
csscapture_py3: kommandot finns inte
csscapture_py3: komut yok
csscapture_py3: nie znaleziono polecenia
csscapture_py3: níor aimsíodh an t-ordú
csscapture_py3: no se encontró la orden
csscapture_py3: no s'ha trobat l'ordre
csscapture_py3: opdracht niet gevonden
csscapture_py3: parancs nem található
csscapture_py3: perintah tidak ditemukan
csscapture_py3: príkaz nenájdený
csscapture_py3: příkaz nenalezen
csscapture_py3: команда не найдена
csscapture_py3: командата не е открита
csscapture_py3: 命令找不到
csscapture_py3: コマンドが見つかりません