refactor: replace the CSS initial property (#180)

Author: ilhan007

packages/main/src/themes/base/DatePicker.less

@@ -9,7 +9,7 @@
 /* Base theme                    */
 /* ============================= */
 
-@_ui5_webcomponents_datepicker_icon_border: initial;
+@_ui5_webcomponents_datepicker_icon_border: none;
 
 :host(ui5-datepicker) {
 	display: inline-block;

packages/main/src/themes/base/MonthPicker.less

@@ -11,8 +11,8 @@
 
 @_ui5_monthpicker_item_background_color: lighten(@sapUiContentForegroundColor, 7);
 @_ui5_monthpicker_item_focus_background_color: darken(@sapUiContentForegroundColor, 5);
-@_ui5_monthpicker_item_border_radius: initial;
-@_ui5_monthpicker_item_border: initial;
+@_ui5_monthpicker_item_border_radius: 0;
+@_ui5_monthpicker_item_border: none;
 @_ui5_monthpicker_item_margin: 1px;
 @_ui5_monthpicker_item_hover_background_color: lighten(@sapUiContentForegroundColor, 7);
 @_ui5_monthpicker_item_focus_after_width: calc(~"100% - 0.375rem");

packages/main/src/themes/base/YearPicker.less

@@ -9,8 +9,8 @@
 /* Base theme                    */
 /* ============================= */
 
-@_ui5_yearpicker_item_border: initial;
-@_ui5_yearpicker_item_border_radius: initial;
+@_ui5_yearpicker_item_border: none;
+@_ui5_yearpicker_item_border_radius: 0;
 @_ui5_yearpicker_item_margin: 1px;
 @_ui5_yearpicker_item_background_color: lighten(@sapUiContentForegroundColor, 7);
 @_ui5_yearpicker_item_hover_background_color: lighten(@sapUiContentForegroundColor, 7);

packages/main/src/themes/sap_belize_hcb/DatePicker.less

@@ -21,4 +21,4 @@
 /* Belize HCB theme              */
 /* ============================= */
 
-@_ui5_webcomponents_datepicker_icon_border: 1px solid transparent;
+@_ui5_webcomponents_datepicker_icon_border: 1px solid transparent;