fix Illustration and IllustrationBlock alt color on dark mode

Author: oxcened

src/components/MDX/MDXComponents.tsx

@@ -239,7 +239,7 @@ function Illustration({
           src={src}
           alt={alt}
           style={{maxHeight: 300}}
-          className="bg-white rounded-lg"
+          className="bg-white text-primary rounded-lg"
         />
         {caption ? (
           <figcaption className="text-center leading-tight mt-4">
@@ -270,7 +270,7 @@ function IllustrationBlock({
   );
   const images = imageInfos.map((info, index) => (
     <figure key={index}>
-      <div className="bg-white rounded-lg p-4 flex-1 flex xl:p-6 justify-center items-center my-4">
+      <div className="bg-white text-primary rounded-lg p-4 flex-1 flex xl:p-6 justify-center items-center my-4">
         <img src={info.src} alt={info.alt} height={info.height} />
       </div>
       {info.caption ? (