Recent Posts FlexSlider – Centering the caption

For my blog I’m using the Recent Post FlexSlider, and it’s working out fine, but I have one problem.
I would like the caption (the area with the title) to be centered vertically.

I’ve been able to center it horizontally, but not vertically.
How do I do that?

/*
 * jQuery FlexSlider v2.2.0
 * https://www.woothemes.com/flexslider/
 *
 * Copyright 2012 WooThemes
 * Free to use under the GPLv2 license.
 * https://www.gnu.org/licenses/gpl-2.0.html
 *
 * Contributing author: Tyler Smith (@mbmufffin)
 */

/* Browser Resets
*********************************/
.flex-container a:active,
.flexslider a:active,
.flex-container a:focus,
.flexslider a:focus {outline: none;}
.slides,
.flex-control-nav,
.flex-direction-nav {margin: 0; padding: 0; list-style: none;}

/* FlexSlider Necessary Styles
*********************************/
.flexslider {margin: 0; padding: 0;}
.flexslider .slides > li {display: none; -webkit-backface-visibility: hidden; margin: auto;} /* Hide the slides before the JS is loaded. Avoids image jumping */
.flexslider .slides img {width: 100%; height: auto; display: inline-block; vertical-align: middle;}
.flex-pauseplay span {text-transform: capitalize;}

/* Clearfix for the .slides element */
.slides:after {content: "020"; display: block; clear: both; visibility: hidden; line-height: 0; height: 0;}
html[xmlns] .slides {display: block;}
* html .slides {height: 1%;}

/* No JavaScript Fallback */
/* If you are not using another script, such as Modernizr, make sure you
 * include js that eliminates this class on page load */
.no-js .slides > li:first-child {display: block;}

/* FlexSlider Default Theme
*********************************/
.flexslider {margin: 0 0 60px; position: relative; zoom: 1;}
.flex-viewport {max-height: 2000px; -webkit-transition: all 1s ease; -moz-transition: all 1s ease; -o-transition: all 1s ease; transition: all 1s ease;}
.loading .flex-viewport {max-height: 300px;}
.flexslider .slides {zoom: 1; margin: 0; overflow: hidden;}
.carousel li {margin-right: 5px;}

/* Direction Nav */
.flex-direction-nav {*height: 0;}
.flex-direction-nav a {width: 30px; height: 30px; margin: -20px 0 0; display: block; background: url('../images/bg_direction_nav.png') no-repeat 0 0; position: absolute; top: 50%; z-index: 10; cursor: pointer; text-indent: -9999px; opacity: 0; -webkit-transition: all .3s ease; font-size: 0px;}
.flex-direction-nav .flex-next {background-position: 100% 0; right: -36px;}
.flex-direction-nav .flex-prev {left: -36px;}
.flexslider:hover .flex-prev {opacity: 0.7; left: 10px;}
.flexslider:hover .flex-next {opacity: 0.7; right: 10px;}
.flexslider:hover .flex-next:hover, .flexslider:hover .flex-prev:hover {opacity: 1;}
.flex-direction-nav .flex-disabled {opacity: 0!important; filter:alpha(opacity=0); cursor: default;}

/* Pause/Play */
.flex-pauseplay a {display: block; width: 20px; height: 20px; position: absolute; bottom: 5px; left: 10px; opacity: 0.8; z-index: 10; overflow: hidden; cursor: pointer; color: #000;}
.flex-pauseplay a:hover  {opacity: 1;}

/* Control Nav */
.flex-control-nav {width: 100%; position: absolute; bottom: -40px; text-align: center;}
.flex-control-nav li {margin: 0 6px; display: inline-block; zoom: 1; *display: inline;}
.flex-control-paging li a {width: 10px; height: 10px; display: block; background: #666; background: rgba(0,0,0,0.5); cursor: pointer; text-indent: -9999px; -webkit-border-radius: 20px; -moz-border-radius: 20px; -o-border-radius: 20px; border-radius: 20px; -webkit-box-shadow: inset 0 0 3px rgba(0,0,0,0.3); -moz-box-shadow: inset 0 0 3px rgba(0,0,0,0.3); -o-box-shadow: inset 0 0 3px rgba(0,0,0,0.3); box-shadow: inset 0 0 3px rgba(0,0,0,0.3);}
.flex-control-paging li a:hover {background: #333; background: rgba(0,0,0,0.7);}
.flex-control-paging li a.flex-active {background: #000; background: rgba(0,0,0,0.9); cursor: default;}

.flex-control-thumbs {margin: 5px 0 0; position: static; overflow: hidden;}
.flex-control-thumbs li {width: 25%; float: left; margin: 0;}
.flex-control-thumbs img {width: 100%; display: block; opacity: 0.7; cursor: pointer;}
.flex-control-thumbs img:hover {opacity: 1;}
.flex-control-thumbs .flex-active {opacity: 1; cursor: default;}

/* Caption Styles */

.flexslider-caption {position: relative; bottom: 90px; max-height: 450px; min-height: 50px; width: 500px; background: rgba(0,0,0,0.3); color: #FFFFFF; overflow: hidden; margin: auto;
display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
}
.flexslider-caption:before {content: ''; height: 100%; display: inline-block; }
.flexslider-caption-inner {margin: 0; padding: 0 10px; display: inline-block; }
.flexslider-caption-inner h3,
.flexslider-caption-inner p {margin: 0; color: #FFFFFF;
    padding-top: 30px;
    padding-right: 30px;
    padding-bottom: 30px;
    padding-left: 30px;}
.flexslider-caption-inner h3 {font-size: 36px;}
.flexslider a {text-decoration: none;}

* Caption Styles */

@media screen and (max-width: 800px) {
  .flex-direction-nav .flex-prev {opacity: 1; left: 10px;}
  .flex-direction-nav .flex-next {opacity: 1; right: 10px;}
}

This is the css of the slider.

I have set min & max height because some titles of my posts are longer so the caption size depends on the title. I would like to keep it that way (instead of heaving a fixed capion size)

This is what it looks like right now:

https://nl.tinypic.com/r/mn2ued/8