I wouldn't use the center html tag to center text. That tag is not valid for html 5. Browsers will likely continue to support deprecated tags like this but it isn't good practice to use them. Instead, use either a css class or inline css with the text-align attribute set to "center". In the case of a slider caption that, for example contains an h1 header and a paragraph, you could use a div wrapper with the center alignment. Example code below:

<div style="text-align:center;">
<h1>This is my caption's slideshow header</h1>
<p>Here is some further explanatory caption text about this slide</p>
</div>