Set a minimum height on the combobox button

to fix captionless button height.

IPython/html/static/notebook/less/widgets.less

@@ -1,129 +1,130 b''
 
 .widget-area {
     page-break-inside: avoid;
     .hbox();
 
     .widget-subarea {
         padding: 0.44em 0.4em 0.4em 1px;
         margin-left: 6px;
         .border-box-sizing();
         .vbox();
         .box-flex2();
 
         .widget-hlabel {
             min-width: 10ex;
             padding-right: 8px;
             text-align: right;
             vertical-align: text-top;
             padding-top: 3px;
         }
 
         .widget-vlabel {
             text-align: center;
             vertical-align: text-bottom;
             padding-bottom: 5px;
         }
 
         .widget-hslider {
             padding-left: 8px;
             padding-right: 5px;
             margin-top: 11px;
 
             width: 348px;
             height: 5px !important;
             overflow: visible !important;
 
             border: 1px solid #CCCCCC;
             background: #FFFFFF;
             .corner-all();
 
             .ui-slider {
                 border: 0px !important;
                 background: none !important;
 
                 .ui-slider-handle {
                     width: 14px !important;
                     height: 28px !important;
 
                     margin-top: -8px !important;
                 }
             }
         }
 
         .widget-vslider {
             border: 1px solid #CCCCCC;
             background: #FFFFFF;
             width: 5px;
             margin-left: 12px;
             padding-bottom: 14px;
             .corner-all();
             height: 250px;
 
             .ui-slider {
                 border: 0px !important;
                 background: none !important;
                 margin-left: -4px;
                 margin-top: 5px;
                 height: 100%;
 
                 .ui-slider-handle {
                     width: 28px !important;
                     height: 14px !important;
                     margin-left: -9px;
                 }
             }
         }
 
         .widget-text {
             width: 350px;
             margin-bottom: 0px;
         }
 
         .widget-numeric-text {
             width: 150px;
         }
 
         .widget-progress {
             width: 363px;
 
             /* Disable progress bar animation */
             .bar {
                 -webkit-transition: none;
                 -moz-transition: none;
                 -ms-transition: none;
                 -o-transition: none;
                 transition: none;
             }
         }
 
         .widget-combo-btn {
             min-width: 138px; /* + 26px drop arrow btn = 164px */
+            min-height: 1ex;
         }
 
         .widget-container {
             .border-box-sizing();
         }
 
         .widget-box {
             .start();
             .widget-container();
             margin: 5px;
         }
 
         .widget-hbox {
             .widget-box();
             .hbox();
         }
 
         .widget-hbox-single {
             .widget-hbox();
             height: 30px;
         }
 
         .widget-vbox-single {
             .widget-box();
             .vbox();
             width: 30px;
         }
     }
 }