make buttons fill width under mob landscape

opentech/static_src/src/sass/apply/abstracts/_mixins.scss

@@ -80,12 +80,19 @@
 
 // Button mixin
 @mixin button($bg, $hover-bg) {
+    width: 100%;
     padding: 10px 60px;
     font-weight: $weight--bold;
     color: $color--white;
+    text-align: center;
     background: $bg;
     transition: color, background, border, $transition;
 
+    @include media-query(mob-landscape) {
+        width: auto;
+        text-align: left;
+    }
+
     &:hover,
     &:active {
         cursor: pointer;

opentech/static_src/src/sass/apply/components/_button.scss

@@ -12,6 +12,7 @@
         .form--filters & {
             width: 100%;
             height: 100%;
+            text-align: center;
         }
     }