[RUBY] When I push to Heroku, I get angry with Precompiling assets failed.

Creating an original application.

ruby '2.6.5' rails '6.0.0' mysql2', '0.5.3'

After pushing to Heroku,

remote:  !
remote:  !     Precompiling assets failed.
remote:  !
remote:  !     Push rejected, failed to compile Ruby app.
remote: 
remote:  !     Push failed
remote: Verifying deploy...

  ![remote rejected] master -> master (pre-receive hook declined)
  error: failed to push some refs to 'https://git.heroku.com/Original app
Name.git'

I got an error.

With a flashy red letter error! I was upset by Mark, but I looked it up right away. By the way, I accessed the production environment, but of course I couldn't update it.

By the way, I guessed that it was probably around assets from the letters of Precompiling assets failed, and went to see if there was an error statement at the top.

Then there was! The one who seems to be the cause of the error!

  remote:        Sass::SyntaxError: Invalid CSS after "...kground-color: ": expected expression (e.g. 1px, bold), was ";"

I searched based on Sass :: SyntaxError: Invalid CSS and the hint of "... kground-color:". For the time being, Sass has no touch, so I looked inside the CSS.

　　 background-color: ;

Nothing. .. ..

When I checked it locally, it was OK without this property, so I deleted it. But why did you write it? ..

Triumphantly after pushing to the master

　　 %  git push heroku master

Then I got the same error again. .. .. Also, since the error amount is the same, I checked all the CSS again.

    left      : 50%;

The symbol is too far away. .. ..

   left: 50%;

Change to here and try again

　　 %  git push heroku master

Then I succeeded! !! Was good! !!

Since I am a beginner, I will cherish each error and solve it.