无效的优化，怎么去除缩放导致的card黑线呢？

src/assets/scss/shuju-card.scss

@@ -38,6 +38,7 @@
 
         &.card-line-t {
             background-image: url(../img/shuju/card/line-t.png);
+            background-size: auto 22px;
             left: 22px;
             right: 240px;
             top: 0;
@@ -45,6 +46,7 @@
         }
         &.card-line-r {
             background-image: url(../img/shuju/card/line-r.png);
+            background-size: 22px auto;
             top: 22px;
             bottom: 22px;
             right: 0;
@@ -52,6 +54,7 @@
         }
         &.card-line-b {
             background-image: url(../img/shuju/card/line-b.png);
+            background-size: auto 22px;
             left: 22px;
             right: 240px;
             bottom: 0;
@@ -59,6 +62,7 @@
         }
         &.card-line-l {
             background-image: url(../img/shuju/card/line-l.png);
+            background-size: 22px auto;
             top: 22px;
             bottom: 22px;
             left: 0;