Gutenberg Blockquote: One

The function of education is to teach one to think intensively and to think critically. Intelligence plus character — that is the goal of true education

Martin Luther King Jr.

CSS

/* ---- BLOCKQUOTE ONE ---- */
/* Reset the theme’s default styling */
.wp-block-quote {
  border: none !important;
  padding: 0 !important;
  margin: 80px auto !important;
  background: transparent !important;
  position: relative;
  text-align: left;
}

/* White masking bar moved here */
.wp-block-quote::before {
  content: "";
  position: absolute;
  width: 80px;
  border: 6px solid white; /* match page background */
  bottom: 36px;
  left: 58px;
  z-index: 2;
}

/* Main quote text */
.wp-block-quote p {
  position: relative;
  color: var(--primary);
  font-size: var(--text-l);
  font-weight: normal;
  line-height: 1.2;
  margin: 0;
  font-style: italic;
  border: 2px solid var(--secondary);
  border-radius: 20px;
  padding: var(--space-l) var(--space-l) var(--space-l) 175px; /* space for big opening mark */
  font-family: var(--text-font-family);
  background: transparent;
}

/* Big opening quotation mark */
.wp-block-quote p::before {
  content: "“";
  position: absolute;
  top: 10px;
  left: 20px;
  font-size: 15rem;
  color: var(--secondary);
  font-family: var(--text-font-family);
  line-height: 1;
  z-index: 1;
}

/* Decorative quarter-circle */
.wp-block-quote p::after {
  content: "";
  position: absolute;
  border: 2px solid var(--secondary);
  border-radius: 0 100% 0 0;
  width: 60px;
  height: 60px;
  bottom: -60px;
  left: 50px;
  border-bottom: none;
  border-left: none;
  z-index: 3;
}

/* Citation styling */
.wp-block-quote cite {
  display: block;
  color: var(--secondary);
	font-family:var(--text-font-family);
  font-size: var(--h4);
  font-weight: 600;
  margin-top: 15px;
  margin-left: 150px;
  padding-left: 12px;
  font-style: normal;
	opacity:1;
}
.wp-block-quote cite:first-letter {
  margin-left: -12px;
}

/* Larger text on bigger screens */
@media (min-width: 600px) {
  .wp-block-quote p {
    font-size: 2.6rem;
    line-height: 1.3;
  }
}
@media (max-width: 600px) {
	.wp-block-quote p::before {
	font-size: 8rem!important;
	top:25px;
	}
	.wp-block-quote p {
		padding: var(--space-l) var(--space-l) var(--space-l) 105px; /* space for big opening mark */
	}
}

Notes

This is an idea adapted from https://wpdean.com/css-blockquote/