You cannot, actually. Unless they have a credit on their blog.
I think you mean usuarios online. Just personalize your code and copy paste it on your info or theme.
You shouldn't steal Tumblr themes! :PP
to get it to infinitive scroll - never ending page go into "customize" then in the "description box" copy and paste this codingthen save.
Making a tumblr theme is not that easy. But there are sites that offers good quality themes, with affordable prices.
It's easy to customize your blog's theme on the Tumblr app for Android. Just go to your blog page and click Edit at the top. From there you can change your theme and customize its colors and fonts
Google "perry the platypus tumblr theme".
Go to the website in Related Links, and copy one of the codes. Then go to your blog, click on 'Edit Theme'. Then click on 'Edit HTML'. Paste the code right before the '</head>' part of your HTML.
Learn HTML.
The best thing to do is to message the user on Tumblr and ask where they found their theme or who made it.
The theme used on that site is called Optica
Search around the theme garden. There should be one there. If not look around the web. There are lots of sites dedicated to tumblr themes.
You go to any online site with cursors, copy the URL of the cursor, then go to the page to customize your tumblr. After that you click on the theme, then the HTML code, and pretty much just paste the code for the cursor at the bottom. Save that, then BAM, cool cursor :)