post thumbnail image size

Hi,

Please try the following css code:

.entry-thumbnail {
    height: auto;
}

.entry-thumbnail img {
    width: 100%;
}

you can use simple custom css plugin to put the code in above.

Where shall i insert this code? I am a total beginner, sorry ??

After you install simple custom css plugin, please go to appearance > custom css. Please put the code in above in the provided textarea.

Wow, that works, amazing!!

But i am stil having the issue with the blog posts that have no image. They just have a blank space instead of the image, while i’d like them NOT having this space at all. Any ideas? Thanks in advance!

Hi,

Those space will always display even there is no thumbnail for the post because that was the default settings for the theme. If you want to modify it, its better if you working with the child theme.