<div class="row">

  <div class="col-12">

    <button type="submit" class="btn btn-primary" name="formPart1" value="1">Etape suivante<i class="fas fa-angle-right ml-2"></i></button>

  </div>

</div>

​

<button type="submit" class="test">test button</button>

.btn {

  box-shadow:none;

  transition-duration: 0.3s !important;

}

​

.btn:hover {

  box-shadow:none;

  filter: brightness(70%);

  transition-duration: 0.3s !important;

}

​

.test {

  padding: 10px 40px;

  margin: 5px;

  background-color: #EE0000;

  color: white;

  border:none;

  border-radius: 5px;

  transition-duration: 0.3s !important;

}

.test:hover {

  filter: brightness(70%);

  transition-duration: 0.3s !important;

}

​