use pre for error node, remove border from it

Author: silverwind

web_src/css/markup/content.css

@@ -542,7 +542,7 @@
 
 .markup-block-error {
   display: block !important; /* override fomantic .ui.form .error.message {display: none} */
-  border: 1px solid var(--color-error-border) !important;
+  border: none !important;
   margin-bottom: 0 !important;
   border-bottom-left-radius: 0 !important;
   border-bottom-right-radius: 0 !important;

web_src/js/markup/common.js

@@ -1,7 +1,7 @@
 export function displayError(el, err) {
   el.classList.remove('is-loading');
-  const errorNode = document.createElement('div');
-  errorNode.setAttribute('class', 'ui message error markup-block-error gt-mono');
+  const errorNode = document.createElement('pre');
+  errorNode.setAttribute('class', 'ui message error markup-block-error');
   errorNode.textContent = err.str || err.message || String(err);
   el.before(errorNode);
   el.setAttribute('data-render-done', 'true');