WordPress/wp-includes/blocks/rss/editor-rtl.css

.wp-block-rss li a>div{
  display:inline;
}

.wp-block-rss__placeholder-form{
  align-items:stretch;
  display:flex;
}
.wp-block-rss__placeholder-form>*{
  margin-bottom:8px;
}
@media (min-width:782px){
  .wp-block-rss__placeholder-form>*{
    margin-bottom:0;
  }
}

.wp-block-rss__placeholder-input{
  align-items:stretch;
  display:flex;
  flex-grow:1;
}
.wp-block-rss__placeholder-input .components-base-control__field{
  align-items:stretch;
  display:flex;
  flex-grow:1;
  margin:0 0 0 8px;
}