Index: src/wp-content/themes/twentytwentyone/assets/sass/04-elements/blockquote.scss
===================================================================
--- src/wp-content/themes/twentytwentyone/assets/sass/04-elements/blockquote.scss	(revision 54271)
+++ src/wp-content/themes/twentytwentyone/assets/sass/04-elements/blockquote.scss	(working copy)
@@ -1,5 +1,4 @@
 blockquote {
-	padding: 0;
 	position: relative;
 	margin: var(--global--spacing-vertical) 0 var(--global--spacing-vertical) var(--global--spacing-horizontal);
 
@@ -19,7 +18,6 @@
 	p {
 		letter-spacing: var(--heading--letter-spacing-h4);
 		font-family: var(--quote--font-family);
-		font-size: var(--quote--font-size);
 		font-style: var(--quote--font-style);
 		font-weight: var(--quote--font-weight);
 		line-height: var(--quote--line-height);
@@ -29,7 +27,6 @@
 	footer {
 		font-weight: normal;
 		color: var(--global--color-primary);
-		font-size: var(--global--font-size-xs);
 		letter-spacing: var(--global--letter-spacing);
 	}
 
@@ -57,7 +54,6 @@
 
 	&:before {
 		content: "\201C";
-		font-size: var(--quote--font-size);
 		line-height: var(--quote--line-height);
 		position: absolute;
 		left: calc(-0.5 * var(--global--spacing-horizontal));
@@ -67,7 +63,6 @@
 	cite,
 	footer {
 		color: var(--global--color-primary);
-		font-size: var(--global--font-size-xs);
 		font-style: var(--quote--font-style-cite);
 	}
 
@@ -79,3 +74,18 @@
 		}
 	}
 }
+
+/* Ony apply the default font size if the user has not selected a size. */
+blockquote:not([class*="font-size"]) {
+	font-size: var(--quote--font-size);
+
+	&:before {
+		font-size: var(--quote--font-size);
+	}
+
+	.wp-block-quote__citation,
+	cite,
+	footer {
+		font-size: var(--global--font-size-xs);
+	}
+}
Index: src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_editor.scss
===================================================================
--- src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_editor.scss	(revision 54271)
+++ src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_editor.scss	(working copy)
@@ -5,7 +5,6 @@
 
 	p {
 		font-family: var(--quote--font-family);
-		font-size: var(--quote--font-size);
 		font-style: var(--quote--font-style);
 		font-weight: var(--quote--font-weight);
 		line-height: var(--quote--line-height);
@@ -17,7 +16,6 @@
 
 	&:before {
 		content: "\201C";
-		font-size: var(--quote--font-size);
 		line-height: var(--quote--line-height);
 		left: calc(-0.5 * var(--global--spacing-horizontal));
 	}
@@ -24,7 +22,6 @@
 
 	.wp-block-quote__citation {
 		color: currentColor;
-		font-size: var(--global--font-size-xs);
 		font-style: var(--quote--font-style-cite);
 
 		.has-background &,
@@ -63,6 +60,8 @@
 		}
 	}
 
+	// This block style has been removed from WordPress core,
+	// the CSS is kept for backwards compatibility.
 	&.is-large,
 	&.is-style-large {
 		padding-left: 0;
Index: src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_style.scss
===================================================================
--- src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_style.scss	(revision 54271)
+++ src/wp-content/themes/twentytwentyone/assets/sass/05-blocks/quote/_style.scss	(working copy)
@@ -3,7 +3,6 @@
 
 	&:before {
 		content: "\201C";
-		font-size: var(--quote--font-size);
 		line-height: var(--quote--line-height);
 		left: 8px;
 	}
@@ -11,7 +10,6 @@
 	.wp-block-quote__citation,
 	cite,
 	footer {
-
 		.has-background &,
 		[class*="background-color"] &,
 		[style*="background-color"] &,
@@ -136,3 +134,19 @@
 		}
 	}
 }
+
+/* Ony apply the default font size if the user has not selected a size. */
+blockquote:not([class*="font-size"]) {
+	font-size: var(--quote--font-size);
+	
+	&:before {
+		font-size: var(--quote--font-size);
+	}
+	
+	.wp-block-quote__citation,
+	cite,
+	footer {
+		font-size: var(--global--font-size-xs);
+	}
+}
+