Good Morning,

Look like you have CSS conflict between your theme and our plugin. The reason for that is your theme is using global styles that overwrite ours.

Can you please give me link to the site so I can check what is going on and provide you a solution? 

Unfortunately I will need to see the calendar live so I can see which classes are making problems. If you can make  a mirror site for me to just check will be great.

Hello there,

There are few global styles that cause the problem and some others that simple don't make sense to me, but I guess thats the author decision.

To fix this go to your Dashboard -> St. Event Calendar -> Fonts & Colors -> Custom Styles and paste this code:

.stec-layout-event .stec-layout-event-preview-left-text-title, .stec-layout-event .stec-layout-event-preview-left-text-date {
    margin-bottom: 0 !important;
}
.stec-layout-agenda .stec-layout-agenda-monthstart-year { margin-bottom: 0 !important; }
.stec-layout-agenda .stec-layout-agenda-monthstart-month {margin-bottom: 0 !important; }
body .stec-layout-event-inner-top-tabs li.active p {  margin-bottom: 0 !important; }
body .stec-layout-event-btn-sec-fontandcolor { line-height: 1.2; }
.stec-layout-agenda .stec-layout-agenda-events-all-load-more p { margin-bottom: 0 !important; }
.stec-layout-event-inner-button-style p {margin-bottom: 0 !important; }
.stec-layout-event-inner-forecast .stec-layout-event-inner-forecast-details .stec-layout-event-inner-forecast-details-left .stec-layout-event-inner-forecast-details-left-forecast .stec-layout-event-inner-forecast-details-left-forecast-top p {
    margin-bottom: 0 !important;
}
.stec-layout-event-inner-forecast .stec-layout-event-inner-forecast-details .stec-layout-event-inner-forecast-details-left .stec-layout-event-inner-forecast-details-left-forecast .stec-layout-event-inner-forecast-details-left-forecast-day > div, .stec-layout-event-inner-forecast .stec-layout-event-inner-forecast-details .stec-layout-event-inner-forecast-details-left .stec-layout-event-inner-forecast-details-left-forecast .stec-layout-event-inner-forecast-details-left-forecast-day p {
     margin-bottom: 0 !important;
}
body .stec-layout-month-daylabel p { margin-bottom: 0 !important; }
body .stec-layout-grid .stec-layout-grid-event-title a { text-decoration: none !important; }
.stec-layout-grid .stec-layout-grid-events-all-load-more p { margin-bottom: 0 !important; }
.stec ul li::before {
  content:none;
}
.stec-layout-event-inner-top-tabs > li p {
  margin-bottom:0 ;
}

Save the changes and check if everything is okay. It's possible to experience more of these conflicts while adding more content, if you see anything just let me know.