I used this tutorial to create the slideshows on my portfolio website. The problem is only on mobile (and doesn't show up with resizing the desktop window/inspector tool on Chrome), where the left scroll button's width is stretching across the whole image. I can't figure out what is causing this in W3School's stylesheet, which I copied into my own stylesheet.
The relevant HTML is:
<button class="w3-button w3-black w3-display-left" onclick="plusDivs(-1)">❮</button>
and relevant CSS (I think) is:
padding: 8px 16px;
transform: translate(0%, -50%);
-ms-transform: translate(-0%, -50%)
There are a few more .w3-buttons in the stylesheet though. I just really don't know where to begin.