String interpolation 7/9 stuck

I am working on string interpolation Sass 7/9, and I am not sure what is wrong with my code below. help please?

stripe-properties: to bottom, 15%, blue, white;

@mixin photo-content($file) {
content: url(#{$file}.jpg);
object-fit: cover;
@mixin stripes($direction, $width-percent, $stripe-color, $stripe-background: #FFF) {
background: repeating-linear-gradient(
$stripe-background ($width-percent - 1),
$stripe-color 1%,
$stripe-background $width-percent

@mixin transform($transformation) {
transform: $transformation;
-webkit-transform: $transformation;
-moz-transform: $transformation;
-ms-transform: $transformation;
-o-transform: $transformation;

@mixin photo-content {
object-fit: cover;

//Add your own mixins here
@mixin transition($time){
transition: $time;
-webkit-transition: $time;
-moz-transition: $time;
-o-transition: $time;
@mixin transform-style($style){
transform-style: $style;
-moz-transform-style: $style;
-o-transform-style: $style;
-ms-transform-style: $style;
-webkit-transform-style: $style;
@mixin backface-visibility($visibility:hidden) {
backface-visibility: $visibility;
-mox-backface-visibility: $visibility;
-ms-backface-visibility: $visibility;
-o-backface-visibility: $visibility;

@include transform-style(preserve-3d);
@include transition(0.4s);
@include transform
width: 300px;
height: 180px;
border: 1px solid black;
display: inline-block;
margin: 20px;
font-family: Roboto, sans-serif;
box-shadow: 1px 1px 2px 2px rgba(0,0,0,.2);
.front, .back {
width: 100%;
height: 100%;
position: absolute;
@include backface-visibility;

.front {
z-index: 3;
font-size: 20px;

.word {
  display: block;
  text-align: center;
  position: relative;
  top: 40%;


.back {
z-index: 1;
word-wrap: break-word;
line-height: 1.6;
@include transform(rotatey(-180deg));

  width: 100%;
  height: 100%;

  .photo {
    @include photo-content('titanosaur');
    width: 60%;
    margin: 0px auto;
   @include stripes($stripe-properties...);



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