.ck-button[data-cke-tooltip-text="Image"] {
  background: url(/sites/default/files/embed_buttons/ck5-picture-icon.png) no-repeat center center !important;
}
.ck-button[data-cke-tooltip-text="Attachment"] {
  background: transparent url(/sites/default/files/embed_buttons/ck5-attachment-icon.png) no-repeat center center !important;
}
.ck-button[data-cke-tooltip-text="Image"]:hover,
.ck-button[data-cke-tooltip-text="Attachment"]:hover {
  background-color: var(--ck-color-button-default-hover-background) !important;
}
.ck-button[data-cke-tooltip-text="Image"] .ck-icon,
.ck-button[data-cke-tooltip-text="Attachment"] .ck-icon {
  display: none;
}