Validate HTML/CSS using Web API

validate.sh

#!/bin/bash

shopt -s globstar

for file in **/*.html; do
  curl -fsS "https://validator.w3.org/nu/?out=gnu" \
    -H "Content-Type: text/html; charset=utf-8"    \
    --data-binary "@$file"                         \
      | { ! grep -z error; }
done

for file in **/*.css; do
  curl -fsS "https://jigsaw.w3.org/css-validator/validator"  \
    -H "Content-Type: multipart/form-data"                   \
    -F warning=2 -F output=text -F "text=<$file"             \
      | { ! grep -z errors; }
done