Create theme_proposal.yml

.github/ISSUE_TEMPLATE/theme_proposal.yml

@@ -0,0 +1,35 @@
+name: Theme Proposal
+description: Suggest a new theme to add to Mermaid.js.
+labels:
+  - "Status: Triage"
+  - "Type: Enhancement"
+
+body:
+  - type: markdown
+    attributes:
+      value: |-
+        Thank you for suggesting a new Theme for Mermaid.js!
+        
+        We are always excited for new ideas to make the library more advanced and useful for people.
+        Please take your time to fill out the below sections with as much detail as you can.
+  - type: textarea
+    attributes:
+      label: Proposal
+      description: A clear and concise description of what theme should be added to Mermaid.js.
+      placeholder: Mermaid.js should add ... because ...
+    validations:
+      required: true
+  - type: textarea
+    attributes:
+      label: Colors
+      description: |-
+        A detailed list of the different colour values to use.
+        A list of currently used variable names can be found [here](https://mermaid-js.github.io/mermaid/#/theming?id=theme-variables-reference-table)
+      placeholder: |-
+        - background: #f4f4f4
+        - primaryColor: #fff4dd
+        - ...
+  - type: textarea
+    attributes:
+      label: Screenshots
+      description: If applicable, add screenshots to show possible examples of how the theme may look like.