[css-align-3] Clarify titles.

Author: fantasai

css-align-3/Overview.bs

@@ -1236,7 +1236,7 @@ Self-Alignment: Aligning the Box Within Its Parent</h2>
 	</div>
 
 <h3 id='justify-self-property'>
-Inline/Main-Axis Alignment: the 'justify-self' property</h3>
+Inline-Axis (or Main-Axis) Alignment: the 'justify-self' property</h3>
 
 	<pre class="propdef">
 	Name: justify-self
@@ -1456,7 +1456,7 @@ Inline/Main-Axis Alignment: the 'justify-self' property</h3>
 	See [[!CSS-GRID-1]] for details.
 
 <h3 id='align-self-property'>
-Block/Cross-Axis Alignment: the 'align-self' property</h3>
+Block-Axis (or Cross-Axis) Alignment: the 'align-self' property</h3>
 
 	<pre class="propdef">
 	Name: align-self
@@ -1789,7 +1789,7 @@ Default Alignment</h2>
 	</div>
 
 <h3 id='justify-items-property'>
-Inline/Main-Axis Alignment: the 'justify-items' property</h3>
+Inline-Axis (or Main-Axis) Alignment: the 'justify-items' property</h3>
 
 	<pre class="propdef">
 	Name: justify-items
@@ -1826,7 +1826,7 @@ Inline/Main-Axis Alignment: the 'justify-items' property</h3>
 	Other values have no special handling and are merely referenced by 'justify-self'.
 
 <h3 id='align-items-property'>
-Block/Cross-Axis Alignment: the 'align-items' property</h3>
+Block-Axis (or Cross-Axis) Alignment: the 'align-items' property</h3>
 
 	<pre class="propdef">
 	Name: align-items