Angular material Could not find Angular Material core theme
Please insert below code into your styles.css which is located in your src folder.
@import "../node_modules/@angular/material/prebuilt-themes/deeppurple-amber.css";
You can select any css under the prebuilt-themes folder.
put that code into your angular-cli.json file
"styles": [
"../node_modules/@angular/material/prebuilt-themes/deeppurple-amber.css"
],
it's works fine for me