New prompt submit button check icon

closes #178

src/scaffolding/check.svg

@@ -0,0 +1 @@
+<svg viewBox="0 0 24 24" xmlns="http://www.w3.org/2000/svg"><path d="M20.773595 5.7280519a1.3077774 1.3077774 0 0 0-1.857043 0L9.1736105 15.484071l-4.0933432-4.10642a1.3364468 1.3364468 0 1 0-1.8570439 1.922432l5.0218651 5.021866a1.3077774 1.3077774 0 0 0 1.8570445 0L20.773595 7.6504847a1.3077774 1.3077774 0 0 0 0-1.9224328z" fill="#fff"/></svg>

src/scaffolding/question.js

@@ -31,11 +31,7 @@ class Question {
     this.submitButton.className = styles.questionSubmitButton;
     this.submitButton.addEventListener('click', this.onsubmitpressclick.bind(this));
 
-    this.submitButtonImage = document.createElement('div');
-    this.submitButtonImage.className = styles.questionSubmitButtonImage;
-
     this.inputContainer.appendChild(this.input);
-    this.submitButton.appendChild(this.submitButtonImage);
     this.inputContainer.appendChild(this.submitButton);
     if (this.textElement) {
       this.inner.appendChild(this.textElement);

src/scaffolding/style.css

@@ -91,7 +91,8 @@
   background: none;
   cursor: pointer;
   color: white;
-  background: var(--sc-accent-color);
+  background-color: var(--sc-accent-color);
+  background-image: url(check.svg);
   overflow: hidden;
 }
 .question-submit-button:focus {
@@ -100,26 +101,6 @@
 .question-submit-button-image {
   width: 100%;
   height: 100%;
-  transform: rotate(-135deg);
-  margin-top: 5px;
-}
-.question-submit-button-image::before {
-  content: '';
-  position: absolute;
-  background-color: currentColor;
-  width: 50%;
-  height: 3px;
-  left: 50%;
-  top: 50%;
-}
-.question-submit-button-image::after {
-  content: '';
-  position: absolute;
-  background-color: currentColor;
-  width: 3px;
-  height: 50%;
-  left: 50%;
-  top: 50%;
 }
 
 .monitor-overlay {