fix(material-experimental/mdc-button): add base css class to all buttons (#18422)

Author: andrewseguin

src/material-experimental/mdc-button/button-base.ts

@@ -35,6 +35,9 @@ export const MAT_BUTTON_HOST = {
   // an unthemed version. If color is undefined, apply a CSS class that makes it easy to
   // select and style this "theme".
   '[class.mat-unthemed]': '!color',
+  // Add a class that applies to all buttons. This makes it easier to target if somebody
+  // wants to target all Material buttons.
+  '[class.mat-mdc-button-base]': 'true',
   'class': 'mat-mdc-focus-indicator',
 };
 
@@ -152,6 +155,9 @@ export const MAT_ANCHOR_HOST = {
   // select and style this "theme".
   '[class.mat-unthemed]': '!color',
   'class': 'mat-mdc-focus-indicator',
+  // Add a class that applies to all buttons. This makes it easier to target if somebody
+  // wants to target all Material buttons.
+  '[class.mat-mdc-button-base]': 'true',
 };
 
 /**

src/material/dialog/dialog.scss

@@ -61,7 +61,8 @@ $mat-dialog-button-margin: 8px !default;
     justify-content: center;
   }
 
-  .mat-button-base + .mat-button-base {
+  .mat-button-base + .mat-button-base,
+  .mat-mdc-button-base + .mat-mdc-button-base {
     margin-left: $mat-dialog-button-margin;
 
     [dir='rtl'] & {

src/material/expansion/expansion-panel.scss

@@ -72,7 +72,7 @@
   justify-content: flex-end;
   padding: 16px 8px 16px 24px;
 
-  button.mat-button-base {
+  button.mat-button-base, button.mat-mdc-button-base {
     margin-left: 8px;
 
     [dir='rtl'] & {