fix(chore): invalid css values

Some CSS values are invalid which this PR fixes.
As a segment has a bottom box shadow by default i kept it for the bottom attached variant while fixing the current invalid assigned value (other elements like message, menu, table dont have a bottom shadow, so the bottom attached variant should also not have some by default

Author: lubber-de

src/definitions/modules/embed.less

@@ -68,7 +68,7 @@
     display: block;
     width: 100%;
     height: 100%;
-    background-color: @placeholderBackground;
+    background: @placeholderBackground;
 }
 
 /* --------------

src/definitions/modules/popup.less

@@ -793,7 +793,7 @@
         box-shadow: @invertedBoxShadow;
     }
     .ui.inverted.popup .header {
-        background-color: @invertedHeaderBackground;
+        background: @invertedHeaderBackground;
         color: @invertedHeaderColor;
     }
     .ui.inverted.popup::before {

src/themes/default/collections/menu.variables

@@ -428,9 +428,7 @@
 @attachedWidth: e(%("calc(100%% + %d)", -@attachedHorizontalOffset * 2));
 @attachedBoxShadow: none;
 @attachedBorder: @borderWidth solid @solidBorderColor;
-@attachedBottomBoxShadow:
-    @boxShadow,
-    @attachedBoxShadow;
+@attachedBottomBoxShadow: @attachedBoxShadow;
 
 /* Resize large sizes */
 @mini: @11px;

src/themes/default/collections/table.variables

@@ -166,9 +166,7 @@
 @attachedWidth: e(%("calc(100%% + %d)", -@attachedHorizontalOffset * 2));
 @attachedBoxShadow: none;
 @attachedBorder: @borderWidth solid @solidBorderColor;
-@attachedBottomBoxShadow:
-    @boxShadow,
-    @attachedBoxShadow;
+@attachedBottomBoxShadow: @attachedBoxShadow;
 
 /* Striped */
 @stripedBackground: rgba(0, 0, 50, 0.02);

src/themes/default/elements/segment.variables

@@ -104,9 +104,7 @@
 @attachedWidth: e(%("calc(100%% + %d)", -@attachedHorizontalOffset * 2));
 @attachedBoxShadow: none;
 @attachedBorder: @borderWidth solid @solidBorderColor;
-@attachedBottomBoxShadow:
-    @boxShadow,
-    @attachedBoxShadow;
+@attachedBottomBoxShadow: @bottomShadow;
 
 /* Inverted */
 @invertedBackground: @black;

src/themes/default/elements/step.variables

@@ -42,7 +42,7 @@
 /* Icon */
 @iconDistance: 1rem;
 @iconSize: 2.5em;
-@iconAlign: middle;
+@iconAlign: center;
 
 /* Title */
 @titleFontFamily: @headerFont;

src/themes/default/globals/site.variables

@@ -649,6 +649,7 @@
 
 /* Differentiating Layers */
 @subtleShadow: 0 1px 2px 0 @borderColor;
+@bottomShadow: 0 2px 1px -1px @borderColor;
 @floatingShadow:
     0 2px 4px 0 rgba(34, 36, 38, 0.12),
     0 2px 10px 0 rgba(34, 36, 38, 0.15);

src/themes/default/views/item.variables

@@ -101,7 +101,7 @@
 
 /* Description */
 @descriptionDistance: 0.6em;
-@descriptionMaxWidth: auto;
+@descriptionMaxWidth: none;
 @descriptionFontSize: 1em;
 @descriptionLineHeight: @lineHeight;
 @descriptionColor: @textColor;