created matminimal custom admin theme based on adminimal

web/themes/custom/matminimal/css/matminimal.css

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+body{
+  /* background-color: red!important; */
+}
+
+details.seven-details{
+  background-color: #333;
+  color:#fff;
+  border-radius: 3px;
+}
+details.seven-details input,
+details.seven-details select{
+  color:#333;
+}
+details.seven-details summary,
+details.seven-details .seven-details__summary:hover,
+details.seven-details .seven-details__summary:focus,
+.seven-details[open] > .seven-details__summary{
+  color:#fff;
+  text-shadow: none;
+}
+
+.adminimal input.form-autocomplete,
+.adminimal input.form-text,
+.adminimal input.form-tel,
+.adminimal input.form-email,
+.adminimal input.form-url,
+.adminimal input.form-search,
+.adminimal input.form-number,
+.adminimal input.form-color,
+.adminimal input.form-file,
+.adminimal input.form-date,
+.adminimal input.form-time,
+.adminimal textarea.form-textarea{
+  border-radius: 3px;
+}
+.adminimal select{
+  border-radius: 3px;
+}
+
+.adminimal .button{
+  background-color: #0071b8;
+  border-radius: 5px;
+}

web/themes/custom/matminimal/matminimal.info.yml

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+name: Matminimal
+type: theme
+description: 'Adminimal based drupal administration theme with material design.'
+core: 8.x
+base theme: adminimal_theme
+
+libraries:
+  - matminimal/global-styling

web/themes/custom/matminimal/matminimal.libraries.yml

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+global-styling:
+  version: VERSION
+  css:
+    theme:
+      css/matminimal.css: {}