Center modal bootstrap (Position fixed under menu fixed on top)

Question

I would like to center a modal window in the center of the screen. Currently the model window is fixed at the top of the window and is placed under my menu which is also fixed at the top. How do I center my modal window in the center of the screen? Here is a screenshot of the current result :

The screen of my Website

Here is also the css / html code used : (it's the classic bootstrap code)

.modal-open {
  overflow: hidden;
}
.modal {
  position: fixed;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  z-index: 1100;
  display: none;
  overflow: hidden;
  -webkit-overflow-scrolling: touch;
  outline: 0;
}
.modal.fade .modal-dialog {
  -webkit-transition: -webkit-transform .3s ease-out;
       -o-transition:      -o-transform .3s ease-out;
          transition:         transform .3s ease-out;
  -webkit-transform: translate(0, -25%);
      -ms-transform: translate(0, -25%);
       -o-transform: translate(0, -25%);
          transform: translate(0, -25%);
}
.modal.in .modal-dialog {
  -webkit-transform: translate(0, 0);
      -ms-transform: translate(0, 0);
       -o-transform: translate(0, 0);
          transform: translate(0, 0);
}
.modal-open .modal {
  overflow-x: hidden;
  overflow-y: auto;
}
.modal-dialog {
  position: relative;
  width: auto;
  margin: 10px;
}
.modal-content {
  position: relative;
  background-color: #fff;
  -webkit-background-clip: padding-box;
          background-clip: padding-box;
  border: 1px solid #999;
  border: 1px solid rgba(0, 0, 0, .2);
  border-radius: 6px;
  outline: 0;
  -webkit-box-shadow: 0 3px 9px rgba(0, 0, 0, .5);
          box-shadow: 0 3px 9px rgba(0, 0, 0, .5);
}
.modal-backdrop {
  position: absolute;
  top: 0;
  right: 0;
  left: 0;
  background-color: #000;
}
.modal-backdrop.fade {
  filter: alpha(opacity=0);
  opacity: 0;
}
.modal-backdrop.in {
  filter: alpha(opacity=50);
  opacity: .5;
}
.modal-header {
  min-height: 16.42857143px;
  padding: 15px;
  border-bottom: 1px solid #e5e5e5;
}
.modal-header .close {
  margin-top: -2px;
}
.modal-title {
  margin: 0;
  line-height: 1.42857143;
}
.modal-body {
  position: relative;
  padding: 15px;
}
.modal-footer {
  padding: 15px;
  text-align: right;
  border-top: 1px solid #e5e5e5;
}
.modal-footer .btn + .btn {
  margin-bottom: 0;
  margin-left: 5px;
}
.modal-footer .btn-group .btn + .btn {
  margin-left: -1px;
}
.modal-footer .btn-block + .btn-block {
  margin-left: 0;
}
.modal-scrollbar-measure {
  position: absolute;
  top: -9999px;
  width: 50px;
  height: 50px;
  overflow: scroll;
}
@media (min-width: 768px) {
  .modal-dialog {
    width: 600px;
    margin: 30px auto;
  }
  .modal-content {
    -webkit-box-shadow: 0 5px 15px rgba(0, 0, 0, .5);
            box-shadow: 0 5px 15px rgba(0, 0, 0, .5);
  }
  .modal-sm {
    width: 300px;
  }
}
@media (min-width: 992px) {
  .modal-lg {
    width: 900px;
  }
}

<!-- Bouton execution modal -->
 <button class="btn btn-primary btn-lg" data-toggle="modal" data-target="#myModal">
   Lancer la modal
 </button>
                    
                     <!-- Modal -->
 <div class="modal fade" id="myModal" tabindex="-1" role="dialog" aria-labelledby="myModalLabel" aria-hidden="true">
    <div class="modal-dialog">
        <div class="modal-content">
 <div class="modal-header">
 <button type="button" class="close" data-dismiss="modal" aria-hidden="true">&times;</button>
 <h4 class="modal-title" id="myModalLabel">Un Savoir-Faire International</h4>
 </div>
    <div class="modal-body">
        <img src="img/savoir-faire-international2.jpg" class="img-responsive"><br>
 "Lorem ipsum dolor sit amet, consectetur adipiscing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
    </div>
        </div><!-- /.modal-content -->
    </div><!-- /.modal-dialog -->
 </div><!-- /.modal -->

Thanks for support ! Jean-Baptiste

Answer 1

Add this css:

.modal {
  text-align: center;
  padding: 0!important;
}

.modal:before {
  content: '';
  display: inline-block;
  height: 100%;
  vertical-align: middle;
  margin-right: -4px;
}

.modal-dialog {
  display: inline-block;
  text-align: left;
  vertical-align: middle;
}