only round CM-gutter corners on outer (left) edge

IPython/frontend/html/notebook/static/notebook/less/codemirror.less

@@ -35,9 +35,10 b''
 }
 
 .CodeMirror-gutters {
-	// This is needed because our cell has rounded corners, otherwise the gutter area square
-	// corner cuts into the rounded cell border.
-	.corner-all;
+  // This is needed because our cell has rounded corners, otherwise the gutter area square
+  // corner cuts into the rounded cell border.
+  border-bottom-left-radius: @corner_radius;
+  border-top-left-radius: @corner_radius;
 }
 
 .CodeMirror pre {

IPython/frontend/html/notebook/static/style/style.min.css

@@ -943,7 +943,7 b' div.output_prompt{color:darkred;margin:0 5px 0 -5px;}'
 .CodeMirror-scroll{overflow-y:hidden;overflow-x:auto;}
 .CodeMirror-lines{padding:0.4em;}
 .CodeMirror-linenumber{padding:0 8px 0 4px;}
-.CodeMirror-gutters{border-radius:4px;}
+.CodeMirror-gutters{border-bottom-left-radius:4px;border-top-left-radius:4px;}
 .CodeMirror pre{padding:0;border:0;-webkit-border-radius:0;-moz-border-radius:0;border-radius:0;}
 .completions{position:absolute;z-index:10;overflow:hidden;border:1px solid #ababab;border-radius:4px;-webkit-box-shadow:0px 6px 10px -1px #adadad;-moz-box-shadow:0px 6px 10px -1px #adadad;box-shadow:0px 6px 10px -1px #adadad;}
 .completions select{background:white;outline:none;border:none;padding:0px;margin:0px;overflow:auto;font-family:monospace;font-size:110%;color:#000000;}