fix(lessons): improve validation completeness and best practices

- 00-basic-selectors: add missing validation message, fix semicolons
- 05-units-variables: replace hex color with named color, use round numbers
- 08-responsive: rename "Flex Grids" to "Responsive Grid" for clarity
- 24-html-progress-meter: add missing high/max/optimum validations
- 32-html-svg: add comprehensive attribute validations for SVG elements

lessons/24-html-progress-meter.json

@@ -86,11 +86,31 @@
 					"value": { "selector": "meter", "attr": "value", "value": "0.8" },
 					"message": "Set <kbd>value=</kbd>\"0.8\" on the meter"
 				},
+				{
+					"type": "attribute_value",
+					"value": { "selector": "meter", "attr": "min", "value": "0" },
+					"message": "Set <kbd>min=</kbd>\"0\" on the meter"
+				},
+				{
+					"type": "attribute_value",
+					"value": { "selector": "meter", "attr": "max", "value": "1" },
+					"message": "Set <kbd>max=</kbd>\"1\" on the meter"
+				},
 				{
 					"type": "attribute_value",
 					"value": { "selector": "meter", "attr": "low", "value": "0.2" },
 					"message": "Set <kbd>low=</kbd>\"0.2\" to define the low threshold"
 				},
+				{
+					"type": "attribute_value",
+					"value": { "selector": "meter", "attr": "high", "value": "0.8" },
+					"message": "Set <kbd>high=</kbd>\"0.8\" to define the high threshold"
+				},
+				{
+					"type": "attribute_value",
+					"value": { "selector": "meter", "attr": "optimum", "value": "1" },
+					"message": "Set <kbd>optimum=</kbd>\"1\" to indicate the optimal value"
+				},
 				{
 					"type": "element_exists",
 					"value": "label",