Symbol boxes same height

a very elegant method is to use the flex box modell:
the align-items: stretch made the trick
put the three iconboxes in a 1/1 container ! give to this 1/1 container the custom class: flex-iconboxes

now put this to your quick css:

/* mediaquery width depends on your settings ( maybe 768px) */

@media (min-width: 990px) {
  .flex_column.flex-iconboxes {
  display: flex;
  flex-flow: nowrap row;
  justify-content: space-between;
  align-items: stretch;
}

.flex_column.flex-iconboxes::before, .flex_column.flex-iconboxes::after {
    display: none;
}

.flex-iconboxes .iconbox {
  flex: 0 1 30%;
  background-color: #e8e8e8 !important;
  border-radius: 5px;
  margin-bottom: 0 !important;
}

.flex-iconboxes .iconbox_content {
  box-shadow: none !important;
}
}

result see here : https://webers-testseite.de/iconboxes-with-equalheight/

if you got more than 3 boxes play with the 30% value ( 4 boxes : less than 24% ) etc