Check the zoom setting on your web browser. In most windows programs you hold CTRL and roll the mouse wheel and the zoom changes - if it doesn't work then look in the Help menu to find how to check it.
If the web browser is definitely at 100% zoom and other sites are all OK, then you have somehow copped a faulty HTML file from ebay - the page layout "settings" are downloaded separately to the actual pages, so if one file gets stuffed up it will affect all web pages from the site.
You can force the web browser to download a complete fresh set of "page components" of the website by doing what is called a "forced refresh"...
Hold down the CTRL key and click on "Refresh" button of the web browser.
Then hold down SHIFt and click on Refresh button.
One of those 2 should take a bit longer to refresh the page, and will probably fix it. If you aren't using Windows, then do a Google for "forced refresh" for your particular browser and operating system.