diff --git a/static/styles/reactions.css b/static/styles/reactions.css
index 7602a2f4af..a0fdbdcd3a 100644
--- a/static/styles/reactions.css
+++ b/static/styles/reactions.css
@@ -78,7 +78,7 @@
 }
 
 .message_reactions .message_reaction:hover {
-    border: thin solid #0088CC;
+    border: 1px solid #0088CC;
 }
 
 .message_reactions .reaction_button:only-child {
@@ -93,13 +93,13 @@
     height: 14px;
     border-radius: 4px;
     padding-left: 0.3em;
-    border: thin solid #bbb;
+    border: 1px solid #bbb;
     padding-right: 0.3em;
     float: left;
 }
 
 .message_reactions .reaction_button:hover {
-    border: thin solid #0088CC;
+    border: 1px solid #0088CC;
     background-color: #eef7fa;
     cursor: pointer;
     opacity: 1.0;
@@ -153,7 +153,7 @@
     margin: 0.1em;
     padding: 0.3em;
     cursor: pointer;
-    border: thin solid white;
+    border: 1px solid white;
     border-radius: 0.5em;
 }
 
diff --git a/tools/lint-all b/tools/lint-all
index 91e8989a0a..53a0f2472d 100755
--- a/tools/lint-all
+++ b/tools/lint-all
@@ -463,6 +463,12 @@ def build_custom_checkers(by_lang):
          'strip': '\n'},
         {'pattern': '{\w',
          'description': "Missing whitespace after '{' in CSS (should be newline)."},
+        {'pattern': ' thin[; ]',
+         'description': "thin CSS attribute is under-specified, please use 1px."},
+        {'pattern': ' medium[; ]',
+         'description': "medium CSS attribute is under-specified, please use pixels."},
+        {'pattern': ' thick[; ]',
+         'description': "thick CSS attribute is under-specified, please use pixels."},
     ]) + whitespace_rules # type: RuleList
     prose_style_rules = [
         {'pattern': '[^\/\#\-\"]([jJ]avascript)', # exclude usage in hrefs/divs