Feedbacks on the "Import data" panel to rebalance the font sizes

[Aurelie-Jallut]

Is your feature request related to a problem? Please describe. text hierarchy helps users understand the panel

Describe the solution you'd like

h3 {
  font-size: 1rem;
}

fieldset legend {
  font-size: 0.9rem;
  padding: 0 5px;
}

.panel .counter {
  display: block;
  margin-top: var(--panel-gutter);
  font-weight: normal;
}

h4 {
  font-size: 0.9rem;
}

.importers ul [type="button"] {
  background: none;
    background-color: rgba(0, 0, 0, 0);
  font-size: 0.75rem;
  border: none;
  width: initial;
  display: inline-block; 
}