I can see that component in crxde but after opening the page in edit mode I can see that component in content tree for 1-2 seconds and then unable to see it. 

No errors

As soon as opening a page in edit mode, a component has been disappearing from content tree. As a result I was unable to add component to the page and author.

Once we have scheduled exam for AD0-E123 Adobe Experience Manager Sites Developer Professional cerification, can we either cancel or change to Adobe experience manager sites developer expert level certification. 

what does it mean to proxying the content in "You can continue to make content updates in AEM and see them reflected in webpack-dev-server, since we are proxying the content." in React SPA . Which is client and which is server in above case.

I have less than 1 year experience in AEM. Would you recommend any AEM beginner level certification?

Yes, I did but it's not getting applied since I'm using  input[type='range']::-webkit-slider-runnable-track  and input[type='range']::-webkit-slider-thumb in css to range slider track and thumb. 

No. I just used "granite/ui/components/coral/foundation/form/colorfield" sling resource type.Here is what I got.And then I'm giving ${properties.color} in style tag. It is applying when it is used for text but I want to use it to change the colors of range slider track and thumb.

I have followed the same but I want content authors to choose colors for range slider track and thumb from dialog box. Even if I add style tag in html to apply the color, it's not applying.

from dialog box they'll choose the colors by changing rgb values