adapt opencollective images to theme background (#9298)

frontend/src/css/custom.css

@@ -26,3 +26,7 @@
 html[data-theme="dark"] .docusaurus-highlight-code-line {
   background-color: rgba(0, 0, 0, 0.3);
 }
+
+.opencollective-image {
+  color-scheme: initial;
+}

frontend/src/pages/community.md

@@ -22,23 +22,32 @@ Shields.io is possible thanks to the people and companies who donate money, serv
 💵 These organisations help keep shields running by donating on OpenCollective. Your organisation can support this project by <a href="https://opencollective.com/shields#sponsor">becoming a sponsor </a>. Your logo will show up here with a link to your website.
 
 <p>
-    <object data="https://opencollective.com/shields/sponsors.svg?avatarHeight=80&width=600" />
+    <object
+        data="https://opencollective.com/shields/sponsors.svg?avatarHeight=80&width=600"
+        class="opencollective-image"
+    ></object>
 </p>
 
 ## Backers
 
 💵 Thank you to all our backers who help keep shields running by donating on OpenCollective. You can support this project by <a href="https://opencollective.com/shields#backer">becoming a backer</a>.
 
 <p>
-    <object data="https://opencollective.com/shields/backers.svg?width=600" />
+    <object
+        data="https://opencollective.com/shields/backers.svg?width=600"
+        class="opencollective-image">
+    </object>
 </p>
 
 ## Contributors
 
 🙏 This project exists thanks to all the nice people who contribute their time to work on the project.
 
 <p>
-    <object data="https://opencollective.com/shields/contributors.svg?width=600" />
+    <object
+        data="https://opencollective.com/shields/contributors.svg?width=600"
+        class="opencollective-image"
+    ></object>
 </p>
 
 ✨ Shields is helped by these companies which provide a free plan for their product or service: