Add two style tweaks to improve tables in code blocks (#738)

Author: waldyrious

.vuepress/styles/index.scss

@@ -7,6 +7,21 @@
   white-space: pre-wrap;
 }
 
+/* Reduce line height in code blocks
+ * to avoid gaps in tables rendered with box-drawing characters
+ */
+.theme-default-content pre,
+.theme-default-content pre[class*=language-] {
+  line-height: 1;
+}
+
+/* Add DejaVu Sans Mono to the list of monospaced fonts.
+ * This allows tables to be rendered seamlessly with box-drawing characters.
+ */
+:root {
+  --font-family-code: Consolas, Monaco, 'Andale Mono', 'DejaVu Sans Mono', 'Ubuntu Mono', monospace;
+}
+
 @media screen and (min-width: 720px) and (max-width: 815px) {
   #docsearch-container {
     width: 150px;