some tiny improvements to filters (mostly hover states) (#5490)

* checkboxes should match filter style

* hover state for more options

* hover state for back trigger

frontend/src/metabase/query_builder/components/filters/FilterPopover.jsx

@@ -261,7 +261,7 @@ export default class FilterPopover extends Component {
                     minWidth: 300
                 }}>
                     <div className="FilterPopover-header text-grey-3 p1 mt1 flex align-center">
-                        <a className="cursor-pointer flex align-center" onClick={this.clearField}>
+                        <a className="cursor-pointer text-purple-hover transition-color flex align-center" onClick={this.clearField}>
                             <Icon name="chevronleft" size={18}/>
                             <h3 className="inline-block">{singularize(table.display_name)}</h3>
                         </a>

frontend/src/metabase/query_builder/components/filters/OperatorSelector.jsx

@@ -74,7 +74,7 @@ export default class OperatorSelector extends Component {
                     </button>
                 )}
                 { !expanded && expandedOperators.length > 0 ?
-                    <div className="text-grey-3 cursor-pointer" onClick={this.expandOperators}>
+                    <div className="text-grey-3 text-purple-hover transition-color cursor-pointer" onClick={this.expandOperators}>
                         <Icon className="px1" name="chevrondown" size={14} />
                         More Options
                     </div>

frontend/src/metabase/query_builder/components/filters/pickers/SelectPicker.jsx

@@ -131,7 +131,10 @@ export default class SelectPicker extends Component {
                            {validOptions.map((option, index) =>
                                <li key={index}>
                                    <label className="flex align-center cursor-pointer p1" onClick={() => this.selectValue(option.key, !checked[option.key])}>
-                                       <CheckBox checked={checked[option.key]} />
+                                       <CheckBox
+                                           checked={checked[option.key]}
+                                           color='purple'
+                                       />
                                        <h4 className="ml1">{this.nameForOption(option)}</h4>
                                    </label>
                                </li>