diff --git a/03 - CSS/css-border-box.md b/03 - CSS/css-border-box.md
new file mode 100644
index 0000000..799820d
--- /dev/null
+++ b/03 - CSS/css-border-box.md	
@@ -0,0 +1,9 @@
+<h1>What does this CSS propoerty do?</h1>
+
+* {
+	box-sizing: border-box;
+}
+
+Essentially, this property makes its so that the padding and border of an HTML element are included in the width and height.  For example, if two divs have the same width defined in the CSS, the border-box property would make it so they are both the same width even if they have different sized borders/padding.
+
+The example above applies it to everything in the HTML.
\ No newline at end of file