wp-includes/blocks/button/editor.css

.wp-block[data-align=center]>.wp-block-button{
  margin-left:auto;
  margin-right:auto;
  text-align:center;
}

.wp-block[data-align=right]>.wp-block-button{
  text-align:right;
}

.wp-block-button{
  cursor:text;
  position:relative;
}
.wp-block-button:focus{
  box-shadow:0 0 0 1px #fff, 0 0 0 3px var(--wp-admin-theme-color);
  outline:2px solid #0000;
  outline-offset:-2px;
}
.wp-block-button[data-rich-text-placeholder]:after{
  opacity:.8;
}

div[data-type="core/button"]{
  display:table;
}

.editor-styles-wrapper .wp-block-button[style*=text-decoration] .wp-block-button__link{
  text-decoration:inherit;
}