DevTools: allow editing custom color palette, move it out of experimental.

Source/devtools/front_end/elements/spectrum.css

 /* https://github.com/bgrins/spectrum */
 :host {
     width: 232px;
     height: 240px;
     -webkit-user-select: none;
 }
 
 :host(.palettes-enabled) {
     height: 271px;
 }
@@ skipping 70 matching lines @@
     top: -1px;
     cursor: pointer;
     width: 13px;
     height: 13px;
     border-radius: 13px;
     background-color: rgb(248, 248, 248);
     box-shadow: 0 1px 4px 0 rgba(0, 0, 0, 0.37);
 }
 
 .swatch {
-    width: 16px;
-    height: 16px;
+    width: 24px;
+    height: 24px;
     margin: 0;
     position: absolute;
-    top: 148px;
-    left: 48px;
+    top: 144px;
+    left: 47px;
     background-image: url(Images/checker.png);
     border-radius: 16px;
 }
 
 .swatch-inner {
     width: 100%;
     height: 100%;
     display: inline-block;
     border-radius: 16px;
 }
@@ skipping 76 matching lines @@
     left: 12px;
     top: 144px;
     cursor: pointer;
 }
 
 .spectrum-palette {
     border-top: 1px solid #dadada;
     position: absolute;
     top: 235px;
     width: 100%;
-    padding-right: 24px;
+    padding: 6px 24px 6px 6px;
     display: flex;
     flex-wrap: wrap;
 }
 
 .spectrum-palette-color {
+    width: 12px;
     height: 12px;
     flex: 0 0 12px;
     display: inline-block;
     border-radius: 2px;
-    margin-left: 12px;
-    margin-top: 12px;
+    margin: 6px;
     cursor: pointer;
 }
 
-.spectrum-palette-color.empty-color {
-    border: 1px solid #dadada;
-}
-
 .spectrum-palette > .spectrum-palette-color {
     transition: transform 100ms cubic-bezier(0, 0, 0.2, 1);
+    border: 1px solid rgba(0, 0, 0, 0.1);
+}
+
+.spectrum-palette > .spectrum-palette-color.empty-color {
+    border-color: transparent;
 }
 
 .spectrum-palette > .spectrum-palette-color:not(.empty-color):hover {
     transform: scale(1.15);
 }
 
-.spectrum-palette > .toolbar {
-    margin-left: 5px;
-    margin-top: 5px;
+.add-color-toolbar {
+    position: absolute;
+    right: 29px;
+    bottom: 5px;
 }
 
 .spectrum-palette-switcher {
     right: 10px;
     top: 235px;
     margin-top: 9px;
     position: absolute;
 }
 
 .palette-panel {
@@ skipping 69 matching lines @@
     width: 100%;
     height: 100%;
 }
 
 .spectrum-contrast-line {
     fill: none;
     stroke: white;
     opacity: 0.7;
     stroke-width: 1.5px;
 }