inherit style instead of duplicating it

IPython/html/static/notebook/less/cell.less

@@ -1,15 +1,16
 div.cell {
     border: 1px solid transparent;
     .vbox();
+    .corner-all();
+    border-width: thin;
+    border-style: solid;
 
     &.selected {
-        .corner-all;
-        border : thin @border_color solid;
+        border-color: @border_color;
     }
     
     &.edit_mode {
-        .corner-all;
-        border : thin green solid;
+        border-color: green;
     }
 }
 

IPython/html/static/style/ipython.min.css

@@ -44,8 +44,8 div.traceback-wrapper{text-align:left;max-width:800px;margin:auto}
 .ansibgpurple{background-color:#f0f}
 .ansibgcyan{background-color:#0ff}
 .ansibggray{background-color:#808080}
-div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch}div.cell.selected{border-radius:4px;border:thin #ababab solid}
-div.cell.edit_mode{border-radius:4px;border:thin #008000 solid}
+div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch;border-radius:4px;border-width:thin;border-style:solid}div.cell.selected{border-color:#ababab}
+div.cell.edit_mode{border-color:#008000}
 div.cell{width:100%;padding:5px 5px 5px 0;margin:0;outline:none}
 div.prompt{min-width:15ex;padding:.4em;margin:0;font-family:monospace;text-align:right;line-height:1.21429em}
 @media (max-width:480px){div.prompt{text-align:left}}div.inner_cell{display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch;-webkit-box-flex:1;-moz-box-flex:1;box-flex:1;flex:1}

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

@@ -1328,8 +1328,8 input.engine_num_input{width:60px}
 .ansibgpurple{background-color:#f0f}
 .ansibgcyan{background-color:#0ff}
 .ansibggray{background-color:#808080}
-div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch}div.cell.selected{border-radius:4px;border:thin #ababab solid}
-div.cell.edit_mode{border-radius:4px;border:thin #008000 solid}
+div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch;border-radius:4px;border-width:thin;border-style:solid}div.cell.selected{border-color:#ababab}
+div.cell.edit_mode{border-color:#008000}
 div.cell{width:100%;padding:5px 5px 5px 0;margin:0;outline:none}
 div.prompt{min-width:15ex;padding:.4em;margin:0;font-family:monospace;text-align:right;line-height:1.21429em}
 @media (max-width:480px){div.prompt{text-align:left}}div.inner_cell{display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;display:flex;flex-direction:column;align-items:stretch;-webkit-box-flex:1;-moz-box-flex:1;box-flex:1;flex:1}