refactor(mini-button): inline variable for display property (#2819)

src/elements/core/styles/mixins/buttons.scss

@@ -99,8 +99,6 @@
 // Default state for icon-button in form-field
 @mixin icon-button-base($host-selector, $button-selector, $icon-selector) {
   #{$host-selector} {
-    --sbb-button-display: flex;
-
     display: inline-block;
     -webkit-tap-highlight-color: transparent;
     height: fit-content;
@@ -120,7 +118,7 @@
       color: var(--sbb-button-color-default-text);
       cursor: pointer;
       user-select: none;
-      display: var(--sbb-button-display);
+      display: flex;
 
       // Renders background and border in the background absolute to enable the hover animation
       &::before {