diff --git a/packages/ui/lib/Button/notes.md b/packages/ui/lib/Button/notes.md
new file mode 100644
index 0000000..a308b5d
--- /dev/null
+++ b/packages/ui/lib/Button/notes.md
@@ -0,0 +1 @@
+- buttons have box-sizing: border-box; by default
diff --git a/packages/ui/lib/TextInput/styles.module.css b/packages/ui/lib/TextInput/styles.module.css
index b3dff5d..5ac502d 100644
--- a/packages/ui/lib/TextInput/styles.module.css
+++ b/packages/ui/lib/TextInput/styles.module.css
@@ -1,4 +1,5 @@
 .textInput {
+  box-sizing: border-box;
   font-size: 1em;
   background: var(--sys42-input-text-background);
   border: var(--sys42-input-text-border-width) solid