at the end of the day, it was inevitable

tests/Helper/CssAsserter.php

@@ -0,0 +1,67 @@
+<?php
+
+namespace Tests\Helper;
+
+use PHPUnit\Framework\TestCase;
+
+/**
+ * Class CssAsserter
+ *
+ * @package Helper
+ */
+class CssAsserter
+{
+
+    /**
+     * @var string
+     */
+    private $styles;
+
+    /**
+     * CssAsserter constructor.
+     *
+     * @param string $styles Raw css style text.
+     */
+    public function __construct($styles)
+    {
+        $this->styles = $styles;
+    }
+
+    /**
+     * @param string $html Raw html.
+     *
+     * @return CssAsserter
+     */
+    public static function createFromHtml($html)
+    {
+        $matches = [];
+        preg_match('#<style>([^<]*)</style>#i', $html, $matches);
+        array_shift($matches);
+
+        return new CssAsserter(implode("\n", $matches));
+    }
+
+    /**
+     * @param string $selector Css selector.
+     *
+     * @return CssAsserter
+     */
+    public function hasSelector($selector)
+    {
+        TestCase::assertRegExp('/'.$selector.'/i', $this->styles);
+
+        return $this;
+    }
+
+    /**
+     * @param string $selector Css selector.
+     *
+     * @return CssPropertiesAsserter
+     */
+    public function with($selector)
+    {
+        $this->hasSelector($selector);
+
+        return new CssPropertiesAsserter(preg_replace('/%s[^\{]*?\{([^\}]*?)\}/i', '$1', $this->styles), $this);
+    }
+}