WordPress/wp-includes/blocks/template-part/editor-rtl.css

.block-editor-template-part__selection-modal{
  z-index:1000001;
}
@media (min-width:600px){
  .block-editor-template-part__selection-modal .components-modal__frame{
    height:calc(100% - 120px);
    width:calc(100% - 32px);
  }
}
@media (min-width:782px){
  .block-editor-template-part__selection-modal .components-modal__frame{
    width:750px;
  }
}
@media (min-width:960px){
  .block-editor-template-part__selection-modal .components-modal__frame{
    height:70%;
  }
}

.block-library-template-part__selection-search{
  background:#fff;
  padding:16px 0;
  position:sticky;
  top:0;
  z-index:1;
}