fix issue #3999, #4001, #4003, #3988, #3987

notebook/static/acc_overwrite.less

@@ -0,0 +1,38 @@
+//This is file created for overwriting some of bootstrap element color in order to satisfiy the color contrast greater than 4.5:1.
+
+.btn-danger{
+    color: #ffffff;
+    background-color: #df0404;
+    border-color: #df0404;
+}
+
+.btn-warning{
+    color: #ffffff;
+    background-color:#b46102;
+    border-color: #b46102;
+}
+
+.close {
+    float: right;
+    font-size: (@font-size-base * 1.5);
+    font-weight: @close-font-weight;
+    line-height: 1;
+    color: @close-color;
+    text-shadow: @close-text-shadow;
+    .opacity(.6);
+  
+    &:hover,
+    &:focus {
+      color: @close-color;
+      text-decoration: none;
+      cursor: pointer;
+      .opacity(1.0);
+}  button& {
+    padding: 0;
+    cursor: pointer;
+    background: transparent;
+    border: 0;
+    -webkit-appearance: none;
+    appearance: none;
+  }
+}

notebook/static/auth/css/override.css

@@ -5,4 +5,4 @@ a hack to deal with our current css styles and no new styling should be added in
 #ipython-main-app {
     padding-top: 50px;
     text-align: center;
-}
+}

notebook/static/style/style.less

@@ -33,3 +33,5 @@
 
 // terminal
 @import "../terminal/less/terminal.less";
+
+@import "../acc_overwrite.less";