use less variable for rounded corner

and allow none in versions comparison

IPython/html/static/notebook/less/celltoolbar.less

@@ -5,7 +5,7 @@
     border: thin solid #CFCFCF;
     border-bottom: none;
     background : #EEE;
-    border-radius : 3px 3px 0px 0px;
+    border-radius : @border-radius-base @border-radius-base 0px 0px;
     width:100%;
     -webkit-box-pack: end;
     height: @celltoolbar-height;

IPython/html/static/notebook/less/textcell.less

@@ -32,10 +32,6 @@ h1,h2,h3,h4,h5,h6 {
     }
 }
 
-div.cell.text_cell.rendered {
-    padding: 0px;
-}
-
 .text_cell.rendered .input_area {
     display: none;
 }

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

@@ -1158,9 +1158,6 @@ h5:hover .anchor-link,
 h6:hover .anchor-link {
   visibility: visible;
 }
-div.cell.text_cell.rendered {
-  padding: 0px;
-}
 .text_cell.rendered .input_area {
   display: none;
 }

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

@@ -9030,9 +9030,6 @@ h5:hover .anchor-link,
 h6:hover .anchor-link {
   visibility: visible;
 }
-div.cell.text_cell.rendered {
-  padding: 0px;
-}
 .text_cell.rendered .input_area {
   display: none;
 }
@@ -9550,7 +9547,7 @@ p {
   border: thin solid #CFCFCF;
   border-bottom: none;
   background: #EEE;
-  border-radius: 3px 3px 0px 0px;
+  border-radius: 4px 4px 0px 0px;
   width: 100%;
   height: 29px;
   padding-right: 4px;

IPython/html/tasks.py

@@ -11,7 +11,7 @@ components_dir = pjoin(static_dir, 'components')
 here = os.path.dirname(__file__)
 
 min_less_version = '1.7.5'
-max_less_version = '1.8.0' # exclusive
+max_less_version = None # exclusive if string
 
 def _need_css_update():
     """Does less need to run?"""
@@ -66,9 +66,9 @@ def _compile_less(source, target, sourcemap, minify=True, verbose=False):
                          % (min_less_version, max_less_version))
     out = out.decode('utf8', 'replace')
     less_version = out.split()[1]
-    if V(less_version) < V(min_less_version):
+    if min_less_version and V(less_version) < V(min_less_version):
         raise ValueError("lessc too old: %s < %s. Use `$ npm install less@X.Y.Z` to install a specific version of less" % (less_version, min_less_version))
-    if V(less_version) >= V(max_less_version):
+    if max_less_version and V(less_version) >= V(max_less_version):
         raise ValueError("lessc too new: %s >= %s. Use `$ npm install less@X.Y.Z` to install a specific version of less" % (less_version, max_less_version))
     
     static_path = pjoin(here, static_dir)