Thick blue line under slider

Hi, I use the featured slider on every page, except the frontpage. On the laptop (Mac) and desktop (windows) it all seems allright. On the iPad and the iPhone I see this thick blue line. You can see it in the added image. An other measure doesn’t make any difference. I tried a height twice as heigh: result: the same. Remarkable: when I see the featured slider on a page on the MacBook there is a little blue line under the slider in the middle of the page. Is it also possible to remove this. I saw this just for going live. After solving this issue the website is ready to go live.