This is my css:
<!-- flexbox-->
<style>
.flexcontainer {
display:flex;
flex-wrap:wrap;
flex-direction:row;
justify-content:flex-start;
align-items:stretch;
}
.left {order:1; background-color:#0091b3; flex-basis:100%; height:300px;padding:35px;}
.right {order:2; background-color:#7a979f;flex-basis:100%; height:300px;padding:35px;}
@media screen and (min-width:600px) {
.flexcontainer {
flex-wrap:nowrap;
}
.left {
flex-basis:50%;
order:1;
}
.right {
flex-basis:50%;
order:2;
}
}
</style>
<!-- end flexbox-->
This is my html:
<div class="flexcontainer">
<div class="left">
<img style="margin:0 auto;display:block;width:80%;height: auto;margin-top:45px;" src="http://offers.premierinc.com/rs/381-NBB-525/images/pc-capitalanalytics_hires-white_720_con.png" alt="calogo" height="15" width="494"><p style="text-align:center; color: #ffc627;font-family: 'Open Sans', Helvetica, Arial, sans-serif; font-size: 38px; font-weight: 400;margin-bottom: 15px">FREE TRIAL</p><p style="text-align:center;font-family: 'Open Sans', Helvetica, Arial, sans-serif;font-size:20px;color:#b4c0c5;">vulputate vel, odio duis, qui vero, nulla suscipit qui in quis dignissim diam ullamcorper feugait, lorem. Ullamcorper adipiscing aliquip. Odio nulla et aliquam, quis facilisi.</p><a style="color: #ffc627; margin 0 auto;font-size:16px;font-weight:700;margin-top:-3px;padding:7px 15px 7px 15px;background-color:#transparent;border: 2px solid #ffc627;border-radius: 7px;line-height: 1.5;cursor: pointer;font-family: 'Open Sans', Helvetica, Arial, sans-serif;text-decoration:none;" href="#">FIND OUT HERE</a>
</div>
<div class="right">
<img style="margin:0 auto;display:block;margin-top:45px;margin-bottom:30px;" src="http://offers.premierinc.com/rs/381-NBB-525/images/hardhat_icon.png" alt="LineItemDetails" height="100" width="100"><p style="text-align:center; color: #ffc627;font-family: 'Open Sans', Helvetica, Arial, sans-serif; font-size: 38px; font-weight: 400;margin-bottom: 15px;line-height:1.25;">WHAT'S YOUR SOLUTION?</p><p style="text-align:center;font-family: 'Open Sans', Helvetica, Arial, sans-serif;font-size:20px;color:#b4c0c5;">vulputate vel, odio duis, qui vero, nulla suscipit qui in quis dignissim diam ullamcorper feugait, lorem. Ullamcorper adipiscing aliquip. Odio nulla et aliquam, quis facilisi.</p><a style="color: #ffc627; margin 0 auto;font-size:16px;font-weight:700;margin-top:-3px;padding:7px 15px 7px 15px;background-color:#transparent;border: 2px solid #ffc627;border-radius: 7px;line-height: 1.5;cursor: pointer;font-family: 'Open Sans', Helvetica, Arial, sans-serif;text-decoration:none;" href="#">FIND OUT HERE</a>
</div>
</div>
That's due to your setting a pixel height of 300 on content that's over 300 pixels tall.
Removing the height settings for .left and .right should do the trick.