feat(welcome): Add variables.

css/_variables.scss

 $welcomePageHeaderBackgroundRepeat: none;
 $welcomePageHeaderBackgroundSize: none;
 $welcomePageHeaderPaddingBottom: 0px;
+$welcomePageHeaderMinHeight: fit-content;
 
 $welcomePageHeaderTextMarginTop: 35px;
 $welcomePageHeaderTextMarginBottom: 35px;
+$welcomePageHeaderTextDisplay: flex;
+$welcomePageHeaderTextWidth: 650px;
 
 $welcomePageHeaderTextTitleMarginBottom: 16px;
 $welcomePageHeaderTextTitleFontSize: 2.5rem;
 $welcomePageHeaderTextDescriptionMarginBottom: 20px;
 $welcomePageHeaderTextDescriptionAlignSelf: inherit;
 
+$welcomePageEnterRoomDisplay: flex;
 $welcomePageEnterRoomWidth: 680px;
 $welcomePageEnterRoomPadding: 25px 30px;
 $welcomePageEnterRoomBorderRadius: 0px;

css/_welcome_page.scss

         align-items: center;
         display: flex;
         flex-direction: column;
-        min-height: fit-content;
+        min-height: $welcomePageHeaderMinHeight;
         overflow: hidden;
         position: relative;
         text-align: center;
 
         .header-text {
-            display: flex;
+            display: $welcomePageHeaderTextDisplay;
             flex-direction: column;
             margin-top: $watermarkHeight + $welcomePageHeaderTextMarginTop;
             margin-bottom: $welcomePageHeaderTextMarginBottom;
             max-width: calc(100% - 40px);
-            width: 650px;
+            width: $welcomePageHeaderTextWidth;
             z-index: $zindex2;
         }
 
         }
 
         #enter_room {
-            display: flex;
+            display: $welcomePageEnterRoomDisplay;
             align-items: center;
             max-width: calc(100% - 40px);
             width: $welcomePageEnterRoomWidth;