Hi, the div that is causing the issues is the following:
<div class="googlepublisherpluginad" style="text-align: center; width: 100%; height: auto; clear: both;">
It appears like you have added a Google Ad plugin that is causing this. Temporarily disable that plugin and then test and I think you will find the issue will go away.
The following is one possible solution which moves the menu/search section to the top of the page and the ad below it.
.site-header {
position: fixed;
top: 0;
}
.googlepublisherpluginad {
margin-top: 70px;
}
.hentry {
padding-top: 1em;
}
If you have not yet done so, I would suggest creating a child theme so that any customizations you make will not be overwritten by a future theme update. Alternately you can use the Edit CSS function in the Jetpack plugin, or use one of the other Custom CSS plugins that will keep CSS changes from being overwritten.
Child Themes
Child Theme creation plugins
Jetpack plugin
Custom CSS plugins