.btn {
    --inside-border-width: 1px;
    --middle-border-width: calc( var(--inside-border-width) + 4px );
    --outside-border-width: calc( var(--middle-border-width) + 1px );
    box-shadow: 
      0 0 0 var(--inside-border-width) var(--tertiary-d-2),
      0 0 0 var(--middle-border-width) var(--tertiary-d-1),
      0 0 0 var(--outside-border-width) var(--tertiary-d-3);
    border-radius: var(--radius-m): 
}

.btn:hover {
    /* Border Stärke  */
    --inside-border-width-hover: 1px;
    --middle-border-width-hover: 0;
    --outside-border-width-hover: 0;
    /* Border Farbe */
    --inside-border-color-hover: var(--tertiary-d-3)
    --middle-border-color-hover: transparent;
    --outside-border-color-hover: transparent;
    box-shadow: 
      0 0 0 var(--inside-border-width-hover) var(--inside-border-color-hover),
      0 0 0 var(--middle-border-width-hover) var(--middle-border-color-hover),
      0 0 0 var(--outside-border-width-hover) var(--outside-border-color-hover);