diff --git a/katex.js b/katex.js
index 81f8908..d6ad0bc 100644
--- a/katex.js
+++ b/katex.js
@@ -94,7 +94,7 @@ var buildGroup = function(style, color, group, prev) {
         var numer = makeSpan("mfracnum " + nstyle.cls(), [
             makeSpan("", [buildGroup(nstyle, color, group.value.numer)])
         ]);
-        var mid = makeSpan("mfracmid", [makeSpan()]);
+        var mid = makeSpan("mfracmid");
         var denom = makeSpan("mfracden " + dstyle.cls(), [
             makeSpan("", [buildGroup(dstyle, color, group.value.denom)])
         ]);
diff --git a/static/katex.css b/static/katex.css
index f4115c8..e468675 100644
--- a/static/katex.css
+++ b/static/katex.css
@@ -98,11 +98,19 @@ big parens
     text-align: center;
 }
 
-.mfracmid > span {
-    background: black;
+.mfracmid:before {
+    border-bottom-style: solid;
+    border-bottom-width: 1px;
+    content: "";
     display: block;
-    height: 0.05em;
-    min-height: 1px;
+}
+
+.mfracmid:after {
+    border-bottom-style: solid;
+    border-bottom-width: 0.05em;
+    content: "";
+    display: block;
+    margin-top: -1px;
 }
 
 .mfracnum > span {
@@ -156,11 +164,3 @@ big parens
 .green { color: #28ae7b; }
 .gray { color: gray; }
 .purple { color: #9d38bd; }
-
-.blue > .mfracmid > span { background: #6495ed; }
-.orange > .mfracmid > span { background: #ffa500; }
-.pink > .mfracmid > span { background: #ff00af; }
-.red > .mfracmid > span { background: #df0030; }
-.green > .mfracmid > span { background: #28ae7b; }
-.gray > .mfracmid > span { background: gray; }
-.purple > .mfracmid > span { background: #9d38bd; }