implemented html version of the OppositeLen scroll

source/Scrolls/TriangleScrolls.mmt

@@ -103,7 +103,35 @@ theory OppositeLen =
 
         // the description verbalizes deducedLineCA, hence must come after its declaration ❙
         meta ?MetaAnnotations?label "OppositeLen" ❙
-        meta ?MetaAnnotations?description s"Given a triangle △${lverb A B C} right-angled at ⊾${lverb C}, the opposite side has length ${lverb deducedLineCA} = tan(${lverb angleB}) ⋅ ${lverb B C}." ❙
+        meta ?MetaAnnotations?description s"<scroll-description title='OppositeLenScroll' alt='Given a triangle △${lverb A B C} right-angled at ⊾${lverb C}, the opposite side has length ${lverb deducedLineCA} = tan(${lverb angleB}) ⋅ ${lverb B C}.'>
+    <span>Given a triangle</span>
+    <math>
+        <mi>&xutri;<!-- △ --></mi>
+        <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?TriangleProblem?A'>${lverb A}</mi>
+        <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?TriangleProblem?B'>${lverb B}</mi>
+        <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?TriangleProblem?C'>${lverb C}</mi>
+    </math>
+    <span>right-angled at</span>
+    <math>
+        <!--<mi>&angrtvbd;</mi>--><!-- ⦝ -->
+        <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?TriangleProblem_RightAngleAtC?rightAngleC'>${lverb rightAngleC}</mi>
+    </math>,<br />
+    <span>the opposite side has length</span>
+    <math>
+        <mi data-solution-id='http://mathhub.info/FrameIT/frameworld?OppositeLen/Solution?deducedLineCA'>${lverb deducedLineCA}</mi>
+        <mo>&equals;</mo>
+        <mrow>
+            <mi>tan</mi>
+            <!--<mo>&#8289;</mo>-->
+            <mo>(</mo>
+            <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?TriangleProblem_AngleAtB?angleB'>${lverb angleB}</mi>
+            <mo>)</mo>
+        </mrow>
+        <mo>&#8290;</mo>
+        <mi dropzone='copy' data-slot-id='http://mathhub.info/FrameIT/frameworld?OppositeLen/Problem?distanceBC'>${lverb distanceBC}</mi>
+    </math>
+    <span>.</span>
+</scroll-description>" ❙
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