Brompton: use font-base for buttons

brompton/style-editor.css

@@ -300,7 +300,7 @@ object {
 	color: #E8E4DD;
 	font-weight: 900;
 	font-family: "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
-	font-family: var(--font-headings, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
+	font-family: var(--font-base, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
 	font-size: 1em;
 	line-height: 1;
 	background-color: #252E36;

brompton/style-rtl.css

@@ -1082,7 +1082,7 @@ input[type="submit"],
 	cursor: pointer;
 	font-weight: 900;
 	font-family: "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
-	font-family: var(--font-headings, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
+	font-family: var(--font-base, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
 	font-size: 1rem;
 	background-color: #252E36;
 	border-radius: 4px;

brompton/style.css

@@ -1082,7 +1082,7 @@ input[type="submit"],
 	cursor: pointer;
 	font-weight: 900;
 	font-family: "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif;
-	font-family: var(--font-headings, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
+	font-family: var(--font-base, "Nunito Sans", -apple-system, BlinkMacSystemFont, "Segoe UI", "Roboto", "Oxygen", "Ubuntu", "Cantarell", "Fira Sans", "Droid Sans", "Helvetica Neue", sans-serif);
 	font-size: 1rem;
 	background-color: #252E36;
 	border-radius: 4px;