diff --git a/.ci/lint_css.sh b/.ci/lint_css.sh
new file mode 100755
index 0000000..9911d67
--- /dev/null
+++ b/.ci/lint_css.sh
@@ -0,0 +1,75 @@
+#!/bin/sh -e
+# Copyright 2021 Oliver Smith
+# SPDX-License-Identifier: GPL-3.0-or-later
+#
+# As of writing, it seems that every existing CSS linter is either written in
+# JS or ruby and has tons of dependencies... so instead of that let's use this
+# simple shell script for now. This script needs find and GNU grep (for -P) and
+# a shell that knows "local".
+
+TOPDIR="$(realpath "$(dirname "$0")/..")"
+CURRENT_FILE=""
+EXIT_CODE=0
+
+# $1: error message
+# $2-n: arguments for grep
+lint() {
+	# shellcheck disable=SC3043
+	local msg="$1"
+	shift
+
+	if grep -q "$@" "$CURRENT_FILE"; then
+		echo "ERROR: $msg"
+		echo "$CURRENT_FILE:"
+		grep -n "$@" "$CURRENT_FILE"
+		echo
+		EXIT_CODE=1
+	fi
+}
+
+lint_spdx() {
+	if ! grep -q "SPDX-License-Identifier" "$CURRENT_FILE"; then
+		echo "ERROR: missing SPDX-License-Identifier in $CURRENT_FILE"
+		echo
+		EXIT_CODE=1
+	fi
+}
+
+lint_file() {
+	lint \
+		"tabs found, indent with 4 spaces instead" \
+		-P '\t'
+
+	lint \
+		"indent with 4 spaces" \
+		-P '^([ ]{1,3}|[ ]{5,7})[a-zA-Z\[\.\/]'
+
+	lint \
+		"spaces at the end of lines are not allowed" \
+		-E ' $'
+
+	lint_spdx
+}
+
+lint_files() {
+	# shellcheck disable=SC2044
+	for CURRENT_FILE in $(find . -name '*.css'); do
+		if ! [ -e "$CURRENT_FILE" ]; then
+			echo "ERROR: no CSS files found in current work dir"
+			exit 1
+		fi
+		lint_file
+	done
+}
+
+cd "$TOPDIR/src"
+lint_files
+
+if [ "$EXIT_CODE" -eq 0 ]; then
+	echo "No linting errors found :)"
+else
+	echo "Please fix the linting errors above and consider configuring your"
+	echo "editor to use the .editorconfig file."
+fi
+
+exit $EXIT_CODE