diff --git a/static/styles/app_components.scss b/static/styles/app_components.scss
index d469faace3..0ffe2943c8 100644
--- a/static/styles/app_components.scss
+++ b/static/styles/app_components.scss
@@ -240,7 +240,7 @@
 
 .new-style .tab-switcher .ind-tab.selected {
     position: relative;
-    background: hsl(0, 0%, 53%);
+    background-color: hsl(0, 0%, 53%);
     color: hsl(0, 0%, 100%);
     border: 1px solid hsl(0, 0%, 46%);
     z-index: 2;
diff --git a/static/styles/billing.scss b/static/styles/billing.scss
index ca51ebb818..9e7780b44d 100644
--- a/static/styles/billing.scss
+++ b/static/styles/billing.scss
@@ -1,10 +1,10 @@
 .billing-upgrade-page {
     font-family: Source Sans Pro, Helvetica, Arial, sans-serif;
-    background: hsl(0, 0%, 98%);
+    background-color: hsl(0, 0%, 98%);
     height: 100vh;
 
     .hero {
-        background: hsl(153, 32%, 55%);
+        background-color: hsl(153, 32%, 55%);
         color: hsl(153, 32%, 55%);
         position: absolute;
         top: 0;
@@ -43,7 +43,7 @@
         border-bottom-left-radius: 4px;
         border-bottom-right-radius: 4px;
         padding: 20px;
-        background: hsl(0, 0%, 100%);
+        background-color: hsl(0, 0%, 100%);
         font-size: 1.1em;
     }
 
@@ -65,7 +65,7 @@
             display: none;
             &:checked {
                 + .box {
-                    background: hsl(153, 32%, 55%);
+                    background-color: hsl(153, 32%, 55%);
                     color: white;
                     border-color: hsl(152, 33%, 39%);
                 }
@@ -74,7 +74,7 @@
         .box {
             width: 120px;
             height: 70px;
-            background: hsl(0, 0%, 94%);
+            background-color: hsl(0, 0%, 94%);
             transition: all .2s ease;
             display: inline-block;
             text-align: center;
@@ -86,7 +86,7 @@
             padding: 30px 20px;
             vertical-align: top;
             &:hover {
-                background: hsl(0, 0%, 91%);
+                background-color: hsl(0, 0%, 91%);
                 border-color: hsl(0, 0%, 80%);
             }
             .schedule-time {
@@ -109,7 +109,7 @@
         padding: 11px 25px 11px 25px;
         font-weight: 400;
         color: white;
-        background: hsl(185, 38%, 55%);
+        background-color: hsl(185, 38%, 55%);
         background: linear-gradient(145deg, rgb(76, 181, 205), rgb(37, 177, 151));
         box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.2);
         border: 0;
@@ -126,13 +126,13 @@
     }
 
     .stripe-button-el:hover {
-        background: rgb(37, 177, 151);
+        background-color: rgb(37, 177, 151);
         box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.3);
     }
 
     .stripe-button-el:active,
     .stripe-button-el:not(:disabled):active {
-        background: rgb(25, 139, 118);
+        background-color: rgb(25, 139, 118);
         span {
             background: 0;
             box-shadow: none;
diff --git a/static/styles/compose.scss b/static/styles/compose.scss
index ca7300f51a..03b057e408 100644
--- a/static/styles/compose.scss
+++ b/static/styles/compose.scss
@@ -69,7 +69,7 @@
 }
 
 .compose_table .message_header_colorblock.message_header_private_message {
-    background: hsl(0, 0%, 27%);
+    background-color: hsl(0, 0%, 27%);
 }
 
 .compose_table .right_part {
@@ -156,7 +156,7 @@ table.compose_table {
     z-index: 2;
     width: 100%;
 
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
 }
 
 #compose-container {
@@ -276,7 +276,7 @@ div[id^="message-edit-send-status"],
     position: relative;
     margin-bottom: 6px;
 
-    background: hsla(152, 51%, 63%, 0.25);
+    background-color: hsla(152, 51%, 63%, 0.25);
     border: 1px solid hsla(0, 0%, 0%, 0.1);
     border-radius: 4px;
 }
diff --git a/static/styles/hotspots.scss b/static/styles/hotspots.scss
index f40da82cb8..34e7808306 100644
--- a/static/styles/hotspots.scss
+++ b/static/styles/hotspots.scss
@@ -11,7 +11,7 @@
     margin: -12.5px 0 0 -12.5px;
     border-radius: 50%;
     position: absolute;
-    background: hsla(196, 100%, 82%, 0.3);
+    background-color: hsla(196, 100%, 82%, 0.3);
     border: 2px solid hsl(215, 47%, 50%);
     top: 50%;
     left: 50%;
@@ -24,7 +24,7 @@
     position: absolute;
     top: 50%;
     left: 50%;
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     border-radius: 50%;
     border: 1px solid hsl(205, 100%, 70%);
     animation: pulsate 1.5s ease-out;
@@ -249,13 +249,13 @@
     max-width: 95%;
     box-shadow: 0 5px 10px rgba(133, 136, 142, 0.1);
     border-radius: 4px;
-    background: hsl(0, 0%, 98%);
+    background-color: hsl(0, 0%, 98%);
     margin: 0 auto;
     position: relative;
 }
 
 .hotspot-inline-top .hotspot-title {
-    background: hsl(168, 100%, 35%);
+    background-color: hsl(168, 100%, 35%);
     margin: 0;
     color: hsl(0, 0%, 100%);
     font-weight: 600;
@@ -280,7 +280,7 @@
 
 #hotspot_intro_reply_icon {
     position: relative;
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     top: 50%;
     transform: perspective(1px) translateY(-75%);
 }
diff --git a/static/styles/input_pill.scss b/static/styles/input_pill.scss
index bfdabee9a3..601a877967 100644
--- a/static/styles/input_pill.scss
+++ b/static/styles/input_pill.scss
@@ -22,14 +22,14 @@
     border: 1px solid hsla(0, 0%, 0%, 0.15);
 
     border-radius: 4px;
-    background: hsla(0, 0%, 0%, 0.07);
+    background-color: hsla(0, 0%, 0%, 0.07);
     cursor: pointer;
 }
 
 .pill-container .pill:focus {
     color: hsl(0, 0%, 100%);
     border: 1px solid hsl(176, 78%, 28%);
-    background: hsl(176, 49%, 42%);
+    background-color: hsl(176, 49%, 42%);
     outline: none;
 }
 
@@ -46,7 +46,7 @@
 .pill-container.not-editable .pill:focus {
     color: inherit;
     border: 1px solid hsla(0, 0%, 0%, 0.15);
-    background: hsla(0, 0%, 0%, 0.07);
+    background-color: hsla(0, 0%, 0%, 0.07);
 }
 
 .pill-container.not-editable .pill .exit {
diff --git a/static/styles/landing-page.scss b/static/styles/landing-page.scss
index cb33c0fc9f..83b56c3eda 100644
--- a/static/styles/landing-page.scss
+++ b/static/styles/landing-page.scss
@@ -839,7 +839,7 @@ nav ul li.active::after {
     margin-top: 0px;
     padding: 12px 20px;
 
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     border: 2px solid hsl(0, 0%, 100%);
 
     font-size: 1.2em;
@@ -1360,7 +1360,7 @@ nav ul li.active::after {
     height: 520px;
     margin: 20px auto;
     padding: 30px 20px;
-    background: rgba(246, 247, 249, 0.6);
+    background-color: rgba(246, 247, 249, 0.6);
     background: linear-gradient(rgba(246, 247, 249, 0.4), rgba(246, 247, 249, 0.9));
     border-radius: 12px;
     box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.02);
@@ -1372,7 +1372,7 @@ nav ul li.active::after {
     font-size: 1.2rem;
     font-weight: 400;
     color: white;
-    background: hsl(185, 38%, 55%);
+    background-color: hsl(185, 38%, 55%);
     background: linear-gradient(145deg, rgb(76, 181, 205), rgb(37, 177, 151));
     box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.3);
     border: 0;
@@ -1387,7 +1387,7 @@ nav ul li.active::after {
 }
 
 .tour .carousel-inner .start-button:hover {
-    background: rgb(37, 177, 151);
+    background-color: rgb(37, 177, 151);
     box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.3);
 }
 
@@ -1546,14 +1546,14 @@ nav ul li.active::after {
     font-weight: 400;
     color: white;
 
-    background: hsl(185, 38%, 55%);
+    background-color: hsl(185, 38%, 55%);
     background: linear-gradient(145deg, rgb(76, 181, 205), rgb(37, 177, 151));
     box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.2);
     border: 0;
 }
 
 .tour .carousel-inner button.call-to-action:hover {
-    background: rgb(37, 177, 151);
+    background-color: rgb(37, 177, 151);
     box-shadow: 0px 3px 10px rgba(0, 0, 0, 0.3);
 }
 
@@ -1598,7 +1598,7 @@ nav ul li.active::after {
     margin-left: 10px;
     text-indent: -999px;
     cursor: pointer;
-    background: hsl(222, 12%, 66%);
+    background-color: hsl(222, 12%, 66%);
     transition: background .1s ease;
 }
 
@@ -1623,7 +1623,7 @@ nav ul li.active::after {
 }
 
 .carousel-indicators li.active {
-    background: hsl(220, 23%, 33%);
+    background-color: hsl(220, 23%, 33%);
 }
 
 .portico-landing.hello .testimonials {
@@ -1798,7 +1798,7 @@ nav ul li.active::after {
     padding: 200px 80px 100px 80px;
     margin-top: -50px;
 
-    background: hsl(177, 52%, 55%);
+    background-color: hsl(177, 52%, 55%);
     background: -webkit-linear-gradient(145deg, hsl(169, 65%, 42%), hsl(191, 55%, 54%));
     background: linear-gradient(145deg, hsl(191, 56%, 55%), hsl(169, 65%, 42%));
 
@@ -1942,7 +1942,7 @@ nav ul li.active::after {
     color: hsl(220, 15%, 66%);
 
     border: 1px solid hsl(220, 15%, 66%);
-    background: transparent;
+    background-color: transparent;
 
     transition: all 0.2s ease;
 }
@@ -2142,7 +2142,7 @@ nav ul li.active::after {
 .portico-landing.why-page .hero {
     padding: 200px 50px 100px 50px;
 
-    background: hsl(153, 32%, 55%);
+    background-color: hsl(153, 32%, 55%);
     color: hsl(0, 0%, 100%);
 }
 
@@ -2198,7 +2198,7 @@ nav ul li.active::after {
 }
 
 .portico-landing.why-page .main blockquote {
-    background: white;
+    background-color: hsl(0, 0%, 100%);
     border-color: hsl(168, 24%, 51%);
     padding: 20px 30px;
     margin-top: 20px;
@@ -2280,7 +2280,7 @@ nav ul li.active::after {
 }
 
 .portico-landing.why-page .testimonials {
-    background: hsl(168, 43%, 24%);
+    background-color: hsl(168, 43%, 24%);
     color: hsl(0, 0%, 100%);
     margin-bottom: 40px;
 }
@@ -2968,7 +2968,7 @@ nav ul li.active::after {
     margin-top: -2px;
     width: calc(100% - 300px - 50px);
 
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     opacity: 0;
     transform: translateY(300px);
 
diff --git a/static/styles/left-sidebar.scss b/static/styles/left-sidebar.scss
index 507c4a41eb..4bb818539f 100644
--- a/static/styles/left-sidebar.scss
+++ b/static/styles/left-sidebar.scss
@@ -110,7 +110,7 @@ ul.filters hr {
 li.active-filter,
 li.active-sub-filter {
     font-weight: 600 !important;
-    background: hsl(202, 56%, 91%);
+    background-color: hsl(202, 56%, 91%);
     position: relative;
 }
 
@@ -171,7 +171,7 @@ li.active-sub-filter {
 .topic-unread-count,
 .private_message_count {
     float: right;
-    background: hsl(105, 2%, 50%);
+    background-color: hsl(105, 2%, 50%);
     padding: 0 4px;
     height: 16px;
     line-height: 16px;
diff --git a/static/styles/media.scss b/static/styles/media.scss
index 0c8f712fdf..3a5d3db715 100644
--- a/static/styles/media.scss
+++ b/static/styles/media.scss
@@ -31,7 +31,7 @@
     }
 
     .column-right.expanded .right-sidebar {
-        background: hsla(0, 0%, 100%, 1.0);
+        background-color: hsla(0, 0%, 100%, 1.0);
         box-shadow: 0px -2px 3px 0px hsla(0, 0%, 0%, 0.1);
         border-left: 1px solid hsl(0, 0%, 86%);
         margin-top: 40px;
@@ -112,7 +112,7 @@
     }
 
     .column-left.expanded .left-sidebar {
-        background: hsla(0, 0%, 100%, 1.0);
+        background-color: hsla(0, 0%, 100%, 1.0);
         box-shadow: 0px 2px 3px 0px hsla(0, 0%, 0%, 0.1);
         border-right: 1px solid hsl(0, 0%, 86%);
         margin-top: 40px;
diff --git a/static/styles/night_mode.scss b/static/styles/night_mode.scss
index a798266374..d5b0e383a8 100644
--- a/static/styles/night_mode.scss
+++ b/static/styles/night_mode.scss
@@ -38,11 +38,11 @@ body.night-mode {
     }
 
     .modal-bg {
-        background: hsl(212, 28%, 18%);
+        background-color: hsl(212, 28%, 18%);
     }
 
     .streams_popover .sp-container {
-        background: transparent;
+        background-color: transparent;
     }
 
     /* this one is because in the app we have blue and in night-mode it should be white. */
@@ -110,7 +110,7 @@ on a dark background, and don't change the dark labels dark either. */
     .pm_recipient .pill-container .pill {
         color: inherit;
         border: 1px solid hsla(0, 0%, 0%, 0.50);
-        background: hsla(0, 0%, 0%, 0.25);
+        background-color: hsla(0, 0%, 0%, 0.25);
         font-weight: 600;
     }
 
@@ -118,7 +118,7 @@ on a dark background, and don't change the dark labels dark either. */
     .pm_recipient .pill-container .pill:focus {
         color: hsl(0, 0%, 100%);
         border: 1px solid hsla(176, 78%, 28%, 0.6);
-        background: hsla(176, 49%, 42%, 0.4);
+        background-color: hsla(176, 49%, 42%, 0.4);
     }
 
     .new-style .button.no-style {
@@ -153,7 +153,7 @@ on a dark background, and don't change the dark labels dark either. */
     .message-header-contents,
     .message_header_private_message .message-header-contents,
     #tab_list li.active {
-        background: hsla(0, 0%, 0%, 0.2);
+        background-color: hsla(0, 0%, 0%, 0.2);
     }
 
     .message-header-contents,
@@ -359,7 +359,7 @@ on a dark background, and don't change the dark labels dark either. */
     }
 
     .user-mention-me {
-        background: hsla(355, 37%, 31%, 1);
+        background-color: hsla(355, 37%, 31%, 1);
         box-shadow: 0px 0px 0px 1px hsla(330, 40%, 20%, 1);
     }
 
@@ -381,7 +381,7 @@ on a dark background, and don't change the dark labels dark either. */
 
     .alert.alert-error,
     .alert.alert-danger {
-        background: hsl(318, 12%, 21%);
+        background-color: hsl(318, 12%, 21%);
         color: inherit;
         border: 1px solid hsl(0, 75%, 65%);
     }
@@ -392,7 +392,7 @@ on a dark background, and don't change the dark labels dark either. */
 
     .alert-box .alert,
     .alert.alert-error {
-        background: hsl(318, 12%, 21%);
+        background-color: hsl(318, 12%, 21%);
         color: inherit;
         border: 1px solid hsl(0, 75%, 65%);
     }
@@ -509,7 +509,7 @@ on a dark background, and don't change the dark labels dark either. */
     }
 
     .ps__rail-y {
-        background: hsl(212, 28%, 18%);
+        background-color: hsl(212, 28%, 18%);
     }
 
     #bots_lists_navbar .active a {
diff --git a/static/styles/popovers.scss b/static/styles/popovers.scss
index e0726acda6..95fde3bc75 100644
--- a/static/styles/popovers.scss
+++ b/static/styles/popovers.scss
@@ -34,7 +34,7 @@
 }
 
 .streams_popover .sp-container {
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     cursor: pointer;
     border: none;
 }
diff --git a/static/styles/portico-signin.scss b/static/styles/portico-signin.scss
index e81e168c72..92ce8a1036 100644
--- a/static/styles/portico-signin.scss
+++ b/static/styles/portico-signin.scss
@@ -478,7 +478,7 @@ html {
     color: hsl(0, 0%, 66%);
     border: 1px solid hsl(0, 0%, 86%);
     border-radius: 4px;
-    background: transparent;
+    background-color: transparent;
 
     transition: color 0.3s ease, border 0.3s ease;
 }
diff --git a/static/styles/portico.scss b/static/styles/portico.scss
index b07749069c..8115dab20e 100644
--- a/static/styles/portico.scss
+++ b/static/styles/portico.scss
@@ -704,7 +704,7 @@ input.text-error {
     list-style-type: none;
     width: 200px;
 
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     padding: 5px 0px;
 
     border-radius: 4px;
@@ -759,7 +759,7 @@ input.text-error {
 }
 
 .portico-header .dropdown ul li:hover a {
-    background: transparent;
+    background-color: transparent;
     color: hsl(0, 0%, 100%);
 }
 
@@ -878,7 +878,7 @@ a.bottom-signup-button {
 }
 
 .table.table-striped {
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     box-shadow: 0px 0px 4px rgba(0, 0, 0, 0.1);
 }
 
@@ -1063,7 +1063,7 @@ input#terminal:checked ~ #tab-terminal {
 
 .integration-lozenge-static:hover {
     box-shadow: none;
-    background: hsl(0, 0%, 93%);
+    background-color: hsl(0, 0%, 93%);
 }
 
 .integration-lozenge .integration-link:hover {
@@ -1537,7 +1537,7 @@ input.new-organization-button {
 .markdown .content {
     padding: 30px;
     max-width: 768px;
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
 }
 
 .markdown a {
diff --git a/static/styles/pygments.scss b/static/styles/pygments.scss
index 2875a35bcf..5a95c6b050 100644
--- a/static/styles/pygments.scss
+++ b/static/styles/pygments.scss
@@ -6,7 +6,7 @@
     background-color: hsl(60, 100%, 90%);
 }
 .codehilite {
-    background: hsl(0, 0%, 97%);
+    background-color: hsl(0, 0%, 97%);
 }
 .codehilite .c {
     color: hsl(180, 33%, 37%);
diff --git a/static/styles/reactions.scss b/static/styles/reactions.scss
index 9a0a732ca9..5e06a40436 100644
--- a/static/styles/reactions.scss
+++ b/static/styles/reactions.scss
@@ -28,7 +28,7 @@
 }
 
 .emoji-popover-emoji.reacted.reaction:focus {
-    background: hsl(195, 55%, 88%);
+    background-color: hsl(195, 55%, 88%);
     outline: none;
 }
 
@@ -267,7 +267,7 @@
 }
 
 .emoji-popover-category-tabs .emoji-popover-tab-item.active {
-    background: hsla(0, 0%, 100%, 0.2);
+    background-color: hsla(0, 0%, 100%, 0.2);
 }
 
 .typeahead .emoji {
diff --git a/static/styles/right-sidebar.scss b/static/styles/right-sidebar.scss
index 8e934574db..cd60ce95be 100644
--- a/static/styles/right-sidebar.scss
+++ b/static/styles/right-sidebar.scss
@@ -153,7 +153,7 @@
 .group-pms-sidebar-entry .count {
     float: right;
     padding: 0 4px;
-    background: hsl(105, 2%, 50%);
+    background-color: hsl(105, 2%, 50%);
     border-radius: 0px;
     color: hsl(0, 0%, 100%);
     font-size: 12px;
diff --git a/static/styles/settings.scss b/static/styles/settings.scss
index 0de23db32e..6cc6ad9cfe 100644
--- a/static/styles/settings.scss
+++ b/static/styles/settings.scss
@@ -375,7 +375,7 @@ input[type=checkbox] + .inline-block {
 }
 
 #settings_page .icon-button:hover {
-    background: hsl(0, 0%, 100%);
+    background-color: hsl(0, 0%, 100%);
     border: 1px solid hsl(0, 0%, 61%);
     color: hsl(0, 0%, 18%);
 }
@@ -422,7 +422,7 @@ input[type=checkbox] + .inline-block {
 }
 
 #settings_page .icon-button.save-button.saving {
-    background: hsl(156, 14%, 40%);
+    background-color: hsl(156, 14%, 40%);
     border-color: hsl(156, 14%, 40%);
 }
 
@@ -559,7 +559,7 @@ input[type=checkbox].inline-block {
     height: auto !important;
     width: auto !important;
 
-    background: transparent;
+    background-color: transparent;
     border-radius: 4px;
     margin-top: 14px;
     margin-left: 10px;
@@ -1590,7 +1590,7 @@ input[type=text]#settings_search {
 }
 
 .subsection-failed-status p {
-    background: hsl(0, 43%, 91%);
+    background-color: hsl(0, 43%, 91%);
     padding: 2px 6px;
     border-radius: 4px;
     margin: 0 0 0 5px;
diff --git a/static/styles/stats.scss b/static/styles/stats.scss
index 637cc63b7f..9bb20ca293 100644
--- a/static/styles/stats.scss
+++ b/static/styles/stats.scss
@@ -158,7 +158,7 @@ hr {
 }
 
 .button:hover {
-    background: hsl(0, 0%, 84%) !important;
+    background-color: hsl(0, 0%, 84%) !important;
 }
 
 .button[data-user="everyone"] {
diff --git a/static/styles/subscriptions.scss b/static/styles/subscriptions.scss
index e0cb972f61..c010d2ef9d 100644
--- a/static/styles/subscriptions.scss
+++ b/static/styles/subscriptions.scss
@@ -607,12 +607,12 @@ form#add_new_subscription {
 
 .stream-row::-moz-selection,
 .stream-row .icon .hashtag::-moz-selection {
-    background: transparent;
+    background-color: transparent;
 }
 
 .stream-row::selection,
 .stream-row .icon .hashtag::selection {
-    background: transparent;
+    background-color: transparent;
 }
 
 .stream-row .check {
@@ -771,7 +771,7 @@ form#add_new_subscription {
     display: flex !important;
     justify-content: center;
     align-items: center;
-    background: hsla(0, 0%, 100%, 0.9);
+    background-color: hsla(0, 0%, 100%, 0.9);
     z-index: 1;
 }
 
diff --git a/static/styles/zulip.scss b/static/styles/zulip.scss
index c227cbf94c..984ef15175 100644
--- a/static/styles/zulip.scss
+++ b/static/styles/zulip.scss
@@ -194,11 +194,11 @@ p.n-margin {
 }
 
 #panels .alert.alert-info {
-    background: hsl(170, 46%, 54%);
+    background-color: hsl(170, 46%, 54%);
 }
 
 #panels .alert.alert-info.red {
-    background: hsl(0, 46%, 54%);
+    background-color: hsl(0, 46%, 54%);
 }
 
 #panels .alert .close {
@@ -880,7 +880,7 @@ td.pointer {
 }
 
 .summary_row_private_message .summary_colorblock {
-    background: hsl(0, 0%, 0%);
+    background-color: hsl(0, 0%, 0%);
 }
 
 .messages-expand,
@@ -1074,7 +1074,7 @@ td.pointer {
 }
 
 .unread-marker-fill {
-    background: hsl(107, 74%, 29%);
+    background-color: hsl(107, 74%, 29%);
     width: 3px;
     height: 100%;
     box-shadow: inset 0px -1px 0px 0px hsl(0, 0%, 100%);
@@ -1709,7 +1709,7 @@ blockquote p {
     height: 12px;
     min-width: 12px;
     line-height: 12px;
-    background: hsl(0, 100%, 20%);
+    background-color: hsl(0, 100%, 20%);
     top: 4px;
     right: 4px;
     border: 1px solid hsl(0, 0%, 93%);
@@ -1849,7 +1849,7 @@ nav a .no-style {
 }
 
 .modal-bg {
-    background: hsl(0, 0%, 98%);
+    background-color: hsl(0, 0%, 98%);
 }
 
 #searchbox {
@@ -2070,7 +2070,7 @@ div.floating_recipient {
 }
 
 .message-header-contents {
-    background: hsl(0, 0%, 88%);
+    background-color: hsl(0, 0%, 88%);
 }
 
 .recipient_row.sticky {
@@ -2252,7 +2252,7 @@ li .message_inline_image img {
     padding: 5px 8px 5px 10px;
     font-size: 12px;
     border-radius: 4px;
-    background: hsl(0, 0%, 0%);
+    background-color: hsl(0, 0%, 0%);
     color: hsl(0, 0%, 100%);
     opacity: 0.7;
 }
@@ -2723,7 +2723,7 @@ div.topic_edit_spinner .loading_indicator_spinner {
 
 .user-group-mention,
 .user-mention {
-    background: hsl(0, 0%, 93%);
+    background-color: hsl(0, 0%, 93%);
     border-radius: 3px;
     padding: 0 0.2em;
     box-shadow: 0px 0px 0px 1px hsl(0, 0%, 80%);
@@ -2741,7 +2741,7 @@ div.topic_edit_spinner .loading_indicator_spinner {
 }
 
 .user-mention-me {
-    background: hsl(112, 88%, 87%);
+    background-color: hsl(112, 88%, 87%);
 }
 
 .alert-word {
@@ -2768,7 +2768,7 @@ div.topic_edit_spinner .loading_indicator_spinner {
     position: absolute;
     left: 0;
     top: 0;
-    background: hsl(0, 0%, 0%);
+    background-color: hsl(0, 0%, 0%);
     z-index: 20000;
 }
 
diff --git a/templates/zerver/app/index.html b/templates/zerver/app/index.html
index ad987bb86a..86b125619c 100644
--- a/templates/zerver/app/index.html
+++ b/templates/zerver/app/index.html
@@ -22,7 +22,7 @@
 <link id="emoji-spritesheet" href="/static/generated/emoji/{{ emojiset }}-sprite.css" rel="stylesheet" type="text/css">
 <style>
     #css-loading {
-    background: white;
+    background-color: white;
     position: fixed;
     height: 100%;
     width: 100%;