feat: Add "transparent" theme (DenverCoder1#462)

Author: DenverCoder1

docs/themes.md

@@ -9,6 +9,7 @@ You can also try out and customize these themes on the [Demo Site](https://strea
 |           `default`           | ![image](https://user-images.githubusercontent.com/107488620/183304039-a1fcf05c-0112-493a-9188-778708dc9e8f.png) |
 |            `dark`             | ![image](https://user-images.githubusercontent.com/107488620/183304038-2788ab5d-4c02-45e9-a724-990f27061c54.png) |
 |        `highcontrast`         | ![image](https://user-images.githubusercontent.com/107488620/183304037-0e54b5e6-f39a-481d-806f-3369d257a391.png) |
+|         `transparent`         | ![image](https://user-images.githubusercontent.com/20955511/221571948-1b69a2cc-87af-4e96-83fa-f01278c22c33.png)  |
 |           `radical`           | ![image](https://user-images.githubusercontent.com/20955511/183303809-eb8fea2f-d56b-4ad3-9f6d-ef55f8812ed2.png)  |
 |            `merko`            | ![image](https://user-images.githubusercontent.com/20955511/183303806-4ce9e5bb-6bd7-4914-a4ff-47edee01bde3.png)  |
 |           `gruvbox`           | ![image](https://user-images.githubusercontent.com/20955511/183303804-95ff960f-ad52-4026-8627-a67f1599cee3.png)  |

src/themes.php

@@ -38,6 +38,18 @@
         "sideLabels" => "#ffffff",
         "dates" => "#c5c5c5",
     ],
+    "transparent" => [
+        "background" => "#0000",
+        "border" => "#E4E2E2",
+        "stroke" => "#E4E2E2",
+        "ring" => "#006AFF",
+        "fire" => "#006AFF",
+        "currStreakNum" => "#0579C3",
+        "sideNums" => "#006AFF",
+        "currStreakLabel" => "#0579C3",
+        "sideLabels" => "#006AFF",
+        "dates" => "#417E87",
+    ],
     "radical" => [
         "background" => "#141321",
         "border" => "#e4e2e2",